b^3-7. 


SIth 


Engineer  Instruction  Manual 
No.  2 


Military  Photography 


Prepared  Under  the  Direction  of 
The  Chief  of  Engineers,  United  States  Army 


1917 


:e,  - - 


- - - A,. 


i-;./ 


r,:: 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 
1917 


A 


Engineer  Instruction  Manual 
No.  2 


Military  Photography 


Prepared  Under  the  Direction  of 
The  Chief  of  Engineers,  United  States  Army 


V 

1917 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 
1917 


TABLE  OF  CONTENTS. 


Page. 

Photographic  equipment  of  Engineer  troops 7 

Lenses 7 

3A  autographic  camera 10 

Directions  for  operating  No.  3A  autographic  camera__' 15 

Instantaneous  exposures 18 

Time  exposures 18 

Some  camera  troubles 20 

3A  Graflex  camera 21 

Distances  and  time  settings,  Table  I 25 

F^ocal  distances,  Table  II 26 

Developing 26 

Fixing  bath 35 

Washing 36 

Drying  film  negatives 36 

After  treatment  of  negatives 36 

In  the  Tropics 38 

Printing 38 

Miscellaneous  formulae,  etc 50 

Military  uses  of  photography 51 

Camera  positions  53 

Special  terms 53 

Adjustments 54 

Plotting 59 

Orienting  the  picture  trace 60 

Locating  points  on  the  map 64 

Determination  of  elevations 65 

Contours  — 

3 


Fig. 


6 


Pig. 


PHOTOGRAPHIC  EQUIPMENT  OF  ENGINEER  TROOPS. 

1.  Each  Engineer  company  is  provided  with  a 3A  auto- 
graphic and  each  regiment  and  mounted  battalion  unit 
with  a 3A  Graflex  camera.  The  remainder  of  the  equip- 
ment is  about  the  same  for  all  units,  except  that  the  Graflex 
camera  outfits  have  about  twice  the  amount  of  supplies 
as  the  other.  Both  of  these  standard  equipments  are 
shown  in  the  plates. 

I.  LENSES.1 

2.  The  most  important  part  of  any  camera  is  its  lens. 
Its  function  is  to  bring  together  the  light  rays  reflected 
from  all  points  of  the  objects  being  photographed  and  to 
concentrate  them  so  as  to  form  an  image  on  the  photo- 
graphic film  or  plate.  A lens  deflects  all  rays  passing 
through  it  in  the  direction  of  its  thickest  portions.  A con- 
vex lens,  therefore,  tends  to  bring  parallel  rays  to  a focus 
or  single  point. 

3.  The  distance  between  this  point  and  the  center  of 
the  lens  is  its  focal  length.  Lenses  are  commonly  de- 
scribed as  being  of  so  many  inches  focus,  which  means  that 
parallel  or  essentially  parallel  rays  are  focused  in  a plane 
located  at  that  distance  from  the  center  of  the  lens.  This 
plane  is  called  the  principal  focal  plane  of  the  camera. 
It  must  not  be  concluded,  however,  that  the  film  is  always 
placed  in  this  plane.  The  nearer  the  lens  is  brought  to 
the  object  to  be  photographed  the  further  back  does  the 
focus  recede.  It  follows,  then,  that  objects  in  different 
planes  or  at  different  distances  from  the  camera  can  not 
be  focused  simultaneously,  unless  all  are  so  distant  that 
rays  of  light  reaching  the  camera  from  them  are  essen- 
tially parallel.^ 

1 The  information  contained  in  Chapters  I to  XI  is  l)ased  largely  on  the  publications  of 
the  Eastman  Kodak  Co.,  and  upon  “ Photography,”  Beeson  and  Williams. 


8 


MILITARY  PHOTOGRAPHY. 


DIAPHRAGMS  OR  STOPS. 

4.  The  negative  record  of  the  image  formed  by  the  lens 
on  a photographic  film  or  plate  is  produced  by  the  chemical 
action  of  light,  and  for  any  one  kind  of  plate  or  film  re-  , 
quires  a very  definite  amount  of  it.  It  follows,  then,  that 
time  of  exposure  can  be  less  as  the  camera  opening  is  in- 
creased or  as  the  plate  is  moved  closer  to  the  lens.  It  also 
follows  that  the  time  of  exposure  can  be  less  on  a bright 
day  than  it  could  be  on  a cloudy  day. 

5.  Most  photographic  lenses  are  fitted  with  metallic 
diaphragms  which  serve  to  control  the  amount  of  liglit 
passing  through  the  lens.  The  size  of  this  opening  is 
usually  expressed  in  terms  of  the  focal  length  of  the  lens 
and  is  usually  abbreviated  as  P.  Thus  P/8  means  a stop 
or  hole  of  a diameter  equal  to  1/8  of  the  distance  between 
the  lens  and  its  principal  focal  plane,  but  the  size  of  the 
stop  might  be  anything  in  inches  and  depends  entirely 
upon  the  focal  length  of  the  lens.  This  system  of  nota- 
tion is  convenient,  because  under  similar  conditions  a 
correct  exposure  for  a plate  will  be  secured,  whatever 
the  focal  length  of  the  lens  may  be,  just  so  long  as  a stop 
of  the  same  proportionate  value  be  used. 

6.  The  reason  for  this  is  as  follows : The  brilliancy  of 
the  illumination  on  the  film  varies  inversely  as  the  square 
of  the  distance  between  the  lens  and  film — that  is,  if  the 
distance  be  doubled  the  illumination  is  decreased  four 
times.  Therefore,  a film  in  the  focal  plane  of  an  8-inch 
lens  is  illuminated  four  times  as  brightly  as  when  placed 
in  the  focal  plane  of  a 16-inch  lens,  if  the  same  size  aper- 
ture in  inches  is  used.  On  the  other  hand,  if  the  stops 
have  the  same  P.  value,  matters  are  balanced,  as  the  long 
focused  lens  has  twice  the  diameter  of  the  other,  and 
therefore  admits  four  times  the  light.  This  is  true  be- 
cause areas  of  circles  vary  directly  as  the  square  of  their 
dimensions. 

7.  The  standard  British  stops  are : 

4 5.6  8 11  16  22  32  45  ^ 64 


MILITAEY  PHOTOGRAPHY. 


9 


They  are  so  graded  that  each  passes  approximately 
half  the  light  of  that  next  above  it  on  the  scale. 

8.  To  find  the  relative  exposure  required  with  the  various 
sizes  of  stops  on  a lens,  compare  the  squares  of  the  denomi- 
nators, which  for  the  first  seven  values  named  above  are 
respectively  16,  31 J,  64,  121,  256,  484,  1024;  or,  reducing 
the  first  to  unity,  1,  2, 4,  8, 16, 32,  64  (approximately) . Ex- 
ample : The  correct  exposure  with  F/5.6  is  8 seconds ; what 
will  it  be  with  F/32  ? The  value  of  E/32  is  to  that  of  E/5.6 

64 

as  64  is  to  2,  so  the  toswer  is  8X-^=256  seconds. 

9.  Most  American  camera  stops  are  numbered  1,  2,  4,  8, 
16,  32,  64,  the  numerals  representing  the  number  of  times 
that  the  exposure  needed  for  the  largest  must  be  multi- 
plied. Thus,  if  stop  No.  32  be  used,  and  two  seconds  is 
the  exposure  required  for  No.  1,  the  time  to  be  given  is 
32  by  2,  or  64.  This  is  the  system  employed  upon  the 
autotime  scale  of  the  3A  camera. 

10.  Auxiliary  uses  of  stops. — Besides  serving  to  control 
the  intensity  of  illumination,  the  stop  has  the  following 
additional  functions: 

(1)  It  keeps  out  rays  that  fall  so  obliquely  on  the 
lens,  that  if  allowed  to  pass  they  would  come  to  a focus 
nearer  the  lens  than  do  the  rays  which  strike  the  lens  less 
obliquely. 

(2)  It  increases  the  depth  of  focus.  The  difficulty 
of  focusing  objects  in  different  planes  increases  with  the 
proximity  of  the  planes  to  the  camera.  By  decreasing 
the  size  of  the  stop  we  can,  as  it  were,  pull  all  the  planes 
together  and  get  a sharp  focus,  even  if  one  object  is  quite* 
close  and  another  a long  way  off.  There  are  many  occa- 
sions on  which  the  photographer  will  find  this  property 
most  valuable. 

(3)  It  extends  the  area  of  sharp  definition  given  by 
the  lens.  Thus,  a lens  which  with  its  diaphragm  full  open 
may  barely  cover  a quarterplate  sharply,  yet  if  stopped 
down  may  cover  a half  plate. 

(4)  It  equalizes  illumination  all  over  the  plate.  With 
a large  stop  the  center  of  the  picture  may  be  much 

9010°— 17 — 2 


10 


MILITARY  PHOTOGRAPHY. 


brighter  than  the  marginal  areas.  If  the  size  of  stop  is 
decreased,  the  diiference  between  central  and  marginal 

illumination  is  de- 
creased also. 

(5)  It  partly  reme- 
dies the  effect  of  cur- 
vature of  field,  which 
tends  to  make  the 
focal  plane  saucer- 
shaped. 

II.  THE  3A  AUTO- 
GRAPHIC CAMERA. 


DESCRIPTION. 


Fig.  3. 


12.  Figures  3 and  4 
show  the  3A  Auto- 
graphic Camera  as 
furnished  to  Engineer 
companies.  It  will  be  noted  that  it  is  equipped  with 
cable  release,  the  autographic  feature,  automatic  shutter, 
and  autotime  scales. 

The  camera  is  opened 
by  pressing  the  con- 
cealed button  ^^a,” 
pulling  the  front 
board  down,  pressing 
the  two  clamps  ^ ^ b ” to- 
gether, and  pulling  the 
front  out  so  as  to  ex- 
tend the  bellows.  The 
camera  maybe  used  in 
either  the  vertical  or 
horizontal  positions 
by  turning  the  finder 
90°  about  a hinge 
provided  for  that 
purpose.  It  is  also 
equipped  with  rising 
and  sliding  front. 

13.  The  autographic  feature. — The  camera  has  a spring 
door  c ” at  the  back  which  covers  a narrow  slot  through 


Fig.  4. 


MILITARY  PHOTOGRAPHY. 


11 


which  writing  is  done  upon  the  red  paper  protecting  the 
film.  This  slot  has  an  automatic  safety  spring  border 
which  operates  when  the  door  is  open  to  press  the  papers 
into  contact  with  the  back  of  the  film,  thus  securing  sharp 
printing  of  the  image  and  preventing  diffusion  of  light 
around  the  edges  of  the  slot.  The  slot  is  so  located  that  the 
writing  normally  comes  between  exposures.  A stylus  or 
smooth-pointed  pencil  should  be  used  in  a vertical  posi- 
tion, care  being  taken  to  press  firmly  on  both  the  up  and 
down  strokes.  After  finishing  the  writing,  the  door  should 
be  left  open  for  printing,  in  accordance  with  the  following 
table,  exposing  the  door  to  the  sky  but  not  to  the  direct 
rays  of  the  sun. 


Out  of  doors. 

Indoor,  close  to  window. 

T^rilliant  light 

2 to  5 seconds 

5 to  7 seconds. 

10  to  15  seconds. 

Dull  light - 

5 to  10  seconds 

Incandescent  light,  distance  2 inches,  30  to  60  seconds. 
Welsbach  light,  distance  6 inches,  30  to  60  seconds. 


14.  Important. — When  the  last  exposure  (No.  6 or  10) 
has  been  made  and  the  separate  autographic  records  have 
been  made  in  accordance  with  the  foregoing  directions, 
turn  the  winding  key  of  the  Kodak  until  the  letter  A ap- 
pears in  the  center  of  the  window.  Then  raise  the  spring 
door  and  insert  any  notes  descriptive  of  the  entire  roll. 
Next  close  the  spring  door  and  finish  winding  the  film 
and  unload. 

15.  The  automatic  shutter. — The  indicator  A should  be 
moved  to  the  point  indicating  the  kind  of  exposure  desired 
and  the  exposure  made  by  pressing  the  lever  or  the  push- 
pin at  the  end  of  the  cable  release  D.  When  the  indicator 
is  at  T the  pushpin  or  lever  must  be  pressed  to  open  the 
shutter  and  again  to  close  it.  When  at  B the  shutter 
closes  the  instant  the  pressure  is  released.  Both  permit 
exposures  to  be  timed  by  a watch.  (Care  must  be  taken 
while  making  time  exposures  not  to  jar  the  camera  when 
manipulating  the  shutter.  When  the  indicator  is  set  at 
any  of  the  numbers  1 to  100,  speeds  ranging  between  one 


12 


MILITARY  PHOTOGRAPHY. 


and  one  hundredth  of  a second  result.  The  cable  release 
is  then  pushed  but  once  for  the  exposure.) 

{Caution, — Do  not  oil  any  part  of  the  shutter.) 

16.  The  autotime  scales, — The  autotime  scales  furnished 
with  this  camera  greatly  simplify  the  work  of  computing 
the  time  of  exposure  and  the  stop  to  be  used  under  vary- 
ing conditions. 

The  following  is  a summary  of  the  settings  for  different 
conditions : 

(1)  The  indicator  should  be  set  at  100  for  all  rapidly 
moving  objects. 

(2)  The  only  time  when  the  camera  can  be  held  in 
the  hand  when  taking  pictures  is  when  the  indicator  is  set 
either  at  100  or  at  25 ; even  then  great  care  must  be  taken 
not  to  move  the  camera  at  the  instant  that  the  shutter  is 
manipulated. 

(3)  Settings  of  upper  scale  for  various  kinds  of  light. 

Brilliant  Use  only  when  sunshine  is  clear  and  in- 
tense and  is  shining  directly  on  the  principal  parts  of  the 
picture. 

Clear  This  is*  used  for  ordinary  sunshine;’  and 
for  intense  sunshine  not  falling  directly  on  the  principal 
parts  of  the  picture  or  when  part  of  the  subject  is  in 
shadow. 

Gray  Hazy  or  dull  sunshine,  best  judged  by  the 
shadow  cast  by  the  sun  which  would  be  called  ^‘half 
shadow,”  a distinct  shadow,  but  not  as  strong  as  with 

brilliant  ” or  clear  ”. 

Dull  ” : Where  a faint  shadow  is  barely  visible. 

Very  dull”:  Sky  completely  overcast;  no  shadow 
of  any  kind  visible. 

(4)  Setting  of  the  lower  scale  (stops  or  diaphragms), 
with  reference  to  subject  and  light. 

The  markings  on  this  scale  are  for  summer  at  mid- 
day. During  the  winter  or  for  the  morning  or  afternoon 
use  the  next  larger  aperture  than  that  indicated. 

64,”  Marine,  clouds,  snow  ” : Use  this  division  where 
any  one  of  these  is  the  principal  subject  an  the  pic- 


MILITARY  PHOTOGRAPHY. 


13 


ture.  Marine — when  view  is  nearly  all  water,  as  with 
ships  or  yachts  at  a long  distance.  Exception : Marine  or 
distant  views  may  be  taken  with  open  lens  and  instanta- 
neous when  conditions  require  it,  such  as  from  decks  of 
moving  vessels  when  the  light  is  poor.  Snow — Use  for 
distant  snow  scenes  only.  Clouds — This  refers  to  no  other 
subject. 

‘‘32,’’  “Distant  view”:  For  landscapes,  mountain 
views,  etc.,  where  the  whole  view  is  removed  some  distance, 
or,  in  other  words,  a general  view,  without  a principal 
object  in  the  foreground. 

“ 16,”  “Average  view  A general  landscape  with 
a principal  object  in  the  foreground,  the  general  land- 
scape being  in  the  nature  of  a background  to  the  prin- 
cipal object.  The  camera  is  always  set  at  100  feet,  but 
the  subject  in  the  foreground  may  be  as  close  to  the  camera 
as  22  feet. 

“8,”  “ Near-view  portrait  Portraits  themselves, 
and  all  other  views  where  the  camera  is  focused  at  less 
than  100  feet,  are  classed  as  general  portraiture. 

{Caution, — When  the  sun  is  shining  and  the  subject  is 
under  cover  or  trees,  so  that  no  sky  is  visible  overhead, 
set  the  lower  pointer  at  “ shadow  ” and  use  “ clear  ” for 
time.) 

“4,”  “ Shadow  ”.  Use  for  all  near  views  where  the 
principal  object  does  not  receive  the  direct  light  of  the 
sun  or  sky.  Use  also  for  near  objects  of  general  red,  green, 
brown,  or  black  color.  “ Moving  objects  ” — Use  for  all 
moving  objects.  Rapidly  moving  objects  require  the  use 
of  ‘ ‘ brilliant  ’ ’ and  ‘ ‘ shadow.  ’ ’ Ordinary  moving  ob j ects, 
such  as  people  walking,  street  traffic,  etc.,  can  be  taken 
with  “ brilliant  ” or  “ clear.” 

In  case  it  is  desired  to  cut  down  the  aperture  in 
order  to  gain  the  full  depth  of  the  focus  of  the  lens,  it  is 
only  necessary  to  move  the  speed  pointer  the  same  number 
of  divisions  toward  “ Very  dull  ” as  you  move  the  aper- 
ture pointer  toward  the  smaller  opening.  You  will  then 
secure  the  same  resultant  exposure,  with  the  increased 


14 


MILITAEY  PHOTOGRAPHY. 


definition  desired.  The  reverse  of  this  is  also  true,  and 
by  this  means  any  aperture  or  any  speed  can  be  used 
within  the  limits  of  proper  exposure. 

5.  Settings  of  the  lower  scale,  with  reference  to  the 
kind  of  exposure. 

No.  4:  For  instantaneous  exposures  on  slightly  cloudy 
days. 

No.  8:  For  all  ordinary  instantaneous  exposures  when 
the  sun  shines. 

No.  16:  For  instantaneous  exposures  when  the  sun- 
light is  unusually  strong  and  there  are  no  heavy  shadows ; 
such  as  in  views  on  the  seashore  or  on  the  water ; also  for 
some  interior  time  exposures. 

Nos.  ^^32/’  ‘^64”:  For  interiors;  never  for  instan- 
taneous exposures. 

17.  Bising  and  sliding  front. — The  No.  3A  Autographic 
Kodaks  are  provided  with  a rising  front,  which  may  be 
utilized  in  cutting  out  an  undesirable  foreground.  The 
front  will  also  slide  to  either  the  right  or  left  (up  and 
down  when  used  for  horizontal  pictures).  The  front  may 
be  raised  or  lowered  by  pressing  in  on  an  eccentric  catch 
just  below  the  milled  elevating  screw,  and  at  the  same 
time  turning  this  to  right  or  left.  When  through  using, 
center  lens  by  moving  the  front  up  and  down  as  the  case 
may  be,  until  the  eccentric  catch  locates  itself  in  notch  in 
standard. 

18.  The  front  can  be  moved  to  the  right  or  left  (up  and 
down  when  Kodak  is  placed  on  its  side  for  a horizontal  ex- 
posure) by  first  releasing  lever  and  then  pressing  down 
on  spring  catch  directly  under  the  lever,  and  at  the  same 
time  sliding  front  in  either  direction  to  the  desired  posi- 
tion. When  through  using,  reverse  the  operation  and 
slide  back  to  the  center  when  the  spring  catch  will  hold 
front  in  position.  Then  turn  lever  to  hold  front  rigid. 

19.  In  order  to  make  a sharp  picture  when  using  the 
rising  front  it  will  be  better  to  use  a small  stop  (No.  32 
or  64),  and  as  this  in  turn  necessitates  a time  exposure  a 
tripod  or  other  firm  support  must  be  provided.  Experi- 


MILITARY  PHOTOGRAPHY. 


15 


ence  alone  can  teach  the  many  ways  in  which  the  rising 
and  sliding  front  may  he  used  for  composing  artistic  pic- 
tures. 

N".  B. — Do  not  fail  to  center  front  before  closing  camera, 
as  otherwise  there  is  danger  of  ruining  the  bellows  during 
folding. 

B.  DIRECTIONS  FOR  OPERATING  THE  3A  AUTOGRAPHIC  CAMERA. 

20.  (a)  Loading, — The  autographic  film  cartridge  is 
made  with  a thin  red  instead  of  the  familiar  thick  red  and 
black  (duplex)  paper.  The  thin  red  paper  is  not  light 
proof  in  itself.  Between  it  and  the  film  is  inserted  a strip 
of  tissue  which  serves  two  purposes — to  supplement  the  red 
paper  in  light  proofing  the  cartridge  and  to  permit  the 
recording,  by  light,  of  the  writing  upon  the  film.  It  should 
be  borne  in  mind  that  after  the  seal  is  broken  care  must  be 
taken  to  keep  the  red  paper  taut  on  the  spool,  as  otherwise 
it  may  slip  and  loosen  sufficiently  to  admit  enough  light  to 
fog  the  film. 

(1)  Take  a position  at  a table  or  at  some  similar  sup- 
port where  the  daylight  is  subdued.  Remove  the  back 
of  the  camera  by  pressing  in  simultaneously  on  the  two 
catches  opposite  its  middle. 

(2)  Pull  out  the  spool  pins  at  both  ends  of  the 
camera,  remo^dng  the  exposed  roll,  and  transfer  the  empty 
spool  to  the  winding  end.  Then  drop  the  film  cartridge 
into  the  other  recess  and  manipulate  it  so  that  the  spool 
pins  may  be  readily  pressed  into  place.  Care  must  be 
taken  to  get  the  top  of  the  cartridge  (plainly  marked 

top  at  the  top  of  the  camera.  (The  top  of  the  camera 
is  its  winding  side.) 

(3)  Remove  the  gummed  slip  that  holds  the  end  of 
the  red  paper ; pass  paper  over  the  two  aluminum  rollers 
and  into  the  roll  slit.  Care  must  be  taken  in  doing  this  so 
that  the  paper  will  draw  straight  and  true.  Next  give  the 
key  one  or  two  turns,  just  enough  to  bend  the  paper  upon 
the  reel. 

(4)  Replace  the  camera  back,  being  careful  to  put 
it  on  right  side  uyi,  remembering  that  the  wide  catch  is  at 


16 


MILITARY  PHOTOGRAPHY. 


the  top.  Snap  the  springs  at  the  top  and  bottom  full  into 
place.  The  camera  back  must  be  handled  carefully  when 
detached,  as  the  slightest  bend  will  make  it  fit  badly  and 
may  result  in  leakage  of  light. 

(5)  As  stated  previously,  the  roller  of  film  is  cov- 
ered with  red  paper.  This  must  be  rolled  oif  before  a pic- 
ture can  be  taken,  turning  the  key  slightly  to  the  left  and 
watching  the  little  celluloid  window  at  the  back  of  the 
camera.  When  about  15  turns  have  been  given,  a hand 
pointing  to  the  first  number  will  appear.  Turn  slowly 
then  until  the  figure  1 registers  with  the  window.  The 
film  is  now  in  a position  for  taking  a picture. 

21.  (1))  Focusing. — (1)  Press  the  concealed  button  and 
push  down  the  bed  of  camera  to  the  limit  of  motion. 

54.  (2)  Set  the  locking  device  for  the  distance  desired, 
grasp  the  springs  at  the  bottom  of  the  front  board  and 
j)ull  out  the  front  to  the  limit. 

22.  hioTE. — The  index  plate  is  scaled  both  by  feet  and 
by  meters  and  care  should  be  taken  not  to  confuse  them? 
Except  when  photographing  at  a distance  of  15  feet 
or  less,  it  is  not  necessary  to  estimate  the  distance  with 
any  more  than  approximate  accuracy ; for  instance,  if  the 
focus  is  set  at  25  feet  (the  usual  distance  for  ordinary 
street  work)  the  sharpest  part  of  the  picture  will  be  the 
objects  at  that  distance  from  the  camera,  but  everything 
from  15  to  35  feet  will  be  in  good  focus.  For  general  street 
work  the  focus  may  be  kept  at  25  feet,  but  where  the  prin- 
cipal object  is  nearer  or  farther  away,  the  focus  should 
be  changed  accordingly.  The  index  plate  is  divided  for 
6,  8,  10,  12,  15,  25,  50,  and  100  feet.  Everything  beyond 
100  feet  is  in  the  100-foot  focus.  Nothing  nearer  than  6 
feet  can  be  focused  without  using  the  portrait  attachment. 

(3)  Aim  the  camera  at  the  object  to  be  photographed 
and  locate  the  image  in  the  finder.  For  a horizontal 
picture  hold  the  camera  as  shown  in  figure  5,  reversing 
the  finder,  as  indicated.  Always  look  into  the  finder 
directly  over  it,  not  at  an  angle.  (If  a ground  focusing 
glass  is  employed  the  image  will  be  located  on  that  instead 
of  in  the  finder.) 


]\riLITAPvY  PHOTOGRAPHY. 


17 


58.  (4)  For  a vertical  exposure  the  camera  must  be 
held  as  shown  in  Fig.  6.  The  finders  give  the  scope  of 
view  and  show  a facsimile  of  the  picture  as  it  will  appear, 
but  on  a reduced  scale.  Any  object  that  does  not  show 
in  the  finder  will  not  show  in  the  picture. 


Pig.  5. 


23.  (c)  Exposing  the  film. — Before  making  an  expo- 
sure with  the  No.  3 A Autographic  Kodak,  either  time  or 
instantaneous,  be  sure  of  four  things : 

First.  That  the  shutter  is  set  properly. 


Fig.  6. 

Second.  That  the  diaphragm  stop  is  set  at  the  proper 
opening. 

Third.  That  the  camera  is  focused. 

Fourth.  That  an  unexposed  section  of  the  film  is  turned 
into  position. 

24.  {d)  Removing  exposed  films. — (1)  When  the  last 
section  of  film  has  been  exposed,  give  the  key  about  five 

'9019°— 17 — 3 


18 


MILITARY  PHOTOGRAPHY. 


half  turns.  Take  a position  as  far  as  possible  from  a 
window,  and  remove  the  back  of  the  camera  as  previously 
described. 

* (2)  Holding  the  red  paper  taut  so  as  to  wind  tightly, 
turn  the  key  until  all  of  the  paper  in  on  the  reel. 
Take  care  to  hold  the  ends  of  the  red  paper  and  sticker 
together  so  as  to  prevent  the  paper  from  loosening  on  the 
^eel.  c-r 

(3)  Pull  out  spool  pin  and  winding  key  and  remove  roll. 

(4)  Fold 'over  half  inch  at  end  of  red  paper  (so  as 
to  make  subsequent  breaking  of  seal  easy)  and  then  seal 
with  sticker.. 

(5)  Wrap  up  exposed  film  at  once  so  as  to  prevent 
possibility  of  light  being  admitted. 

(6)  Transfer  the  empty  spool  to  the  winding  side 
of  the  camera  and  reload  as  previously  described. 

INSTANTANEOUS  EXPOSURES. 

25.  The  ^object  must  be  in  the  broad  open  sunlight  but 
the  camera  should  not  be.  The  sun  should  be  behind  the 
back  or  over  the  shoulder  of  the  operator.  For  all  ordi- 
nary out-door  work  when  the  sun  is  very  bright,  use  stop 
No.  F/11.  If  a smaller  stop  be  used,  the  light  will  be 
so  much  reduced  that  it  will  not  sufficiently  impress  the 
image  on  the  film  and  failure  will  result. 

26.  No.  16  may,be  used  for  marine  views  with  unusually 
strong  sunlight. 

■ TIME  EXPOSURES. 

27.  (a)  Interiors. — (1)  Place  the  camera  on  some  firm 
support  and  so  that  the  finder  will  embrace  the  view  de- 
sired. It  sliould  not  be  pointed  directly  at  a window,  as 
the  glare  will  blur  the  picture.  If  all  the  windows  can  not 
be  avoided,  pull  down  the  shades  of  such  as  come  within 
the  range  of  view. 

. (2)  Set  the  shutter  at  T and  the  stop  at  the  proper 
point.  Press  the  push  pin  once  to  open  and  again  to  close 
the.  shutter.  Time  the  exposure  with  a watch. 

^'(3)  After  making  the  autographic  record,  turn  a new 
film  into  position. 

(4)  Time  required  for  interior  exposures. 


MILITARY  PHOTOGRAPHY. 


19 


28.  The  following  table  gives  the  time  of  exposure  re- 
quired under  varying  conditions  of  light  with  the  stop  No. 
16  in  the  lens.  This  means  that  with  No.  8 stop  the  time 
of  exposure  is  cut  in  half,  and  with  128  should  be  multi- 
plied by  8.  It  should  be  borne  in  mind  that  the  smaller 
the  stop  the  sharper  the  picture.  As  a rule  No.  16  will 
give  best  results  for  interiors. 

White  walls  and  more  than  one  window : 

Bright  sun  outside,  4 seconds. 

Hazy  sun,  10  seconds. 

Cloudy  bright,  20  seconds. 

Cloudy  dull,  40  seconds. 

White  walls  and  only  one  window: 

Bright  sun  outside,  6 seconds. 

Hazy  sun,  15  seconds. 

Cloudy  bright,  30  seconds. 

Cloudy  dull,  60  seconds. 

Medium  colored  walls  and  hangings  and  more  than  one  window: 

Bright  sun  outside,  8 seconds. 

Hazy  sun,  20  seconds. 

Cloudy  bright,  40  seconds. 

Cloudy  dull,  80  seconds. 

Medium  colored  walls  and  hangings  and  only  one  window: 

Bright  sun  outside,  12  seconds. 

Hazy  sun,  30  seconds.  ^ 

Cloudy  bright,  60  seconds. 

Cloudy  dull,  120  seconds. 

Dark  colored  walls  and  hangings  and  more  than  one  window: 

Bright  sun  outside,  20  seconds. 

Hazy  sun,  40  seconds. 

Cloudy  bright,  80  seconds. 

Cloudy  dull,  2 minutes,  40  seconds. 

Dark  colored  walls  and  hangings  and  only  one  window : 

Bright  sun  outside,  40  seconds. 

Hazy  sun,  80  seconds. 

Cloudy  bright,  2 minutes,  40  seconds. 

Cloudy  dull,  5 minutes,  20  seconds. 


29.  The  foregoing  is  calculated  for  rooms  whose  win- 
dows get  the  direct  light  from  the  sky,  and  for  hours  from 
3 hours  after  sunrise  until  3 hours  before  sunset. 

30.  If  earlier  or  later,  the  time  should  be  increased. 

31.  (&)  Time  exposures  in  the  open  air. — When  the 
stop  No.  128  or  F/45  is  in  the  lens,  the  light  admitted  is 
so  much  reduced  that  time  exposures  may  be  made  out  of 
doors  the  same  as  interiors.  The  exposure,  however,  must 


20 


MILITARY  PHOTOGRAPHY. 


be  much  shorter  and  should  be  made  with  the  shutter  indi- 
cator set  at  B.” 

With  sunshine,  k second. 

With  light  clouds,  from  1 to  1 second  will  be  sufficient. 

With  heavy  clouds,  from  2 to  5 seconds  will  be  required. 

32.  The  above  is  calculated  for  the  same  hours  as  men- 
tioned for  interiors  and  for  objects  in  the  open  air.  For 
other  hours  or  for  objects  in  the  shadow,  under  porches 
or  under  trees,  no  accurate  directions  can  be  given ; experi- 
ence only  can  teach  the  proper  exposures. 

33.  Time  exposures  can  not  be  made  while  the  kodak  is 
held  in  the  hand.  Always  place  it  upon  some  firm  sup- 
port, such  as  a tripod,  chair,  or  table. 

SOME  CAMERA  TROUBLES  AND  HOW  TO  ELIMINATE  THEM. 

34.  {a)  Dimmed  finders  and  how  to  make  them  bright 
again. — For  causes  not  always  thoroughly  understood, 
glass  will  sometimes  sweat  ” to  such  an  extent  as  to  cover 
itself  with  a film,  which  will  decrease  the  amount  of  light 
passing  through  it  or  reflected  from  it.  Whatever  the 
cause  the  result  is  the  occasional  dimming  of  finders  and 
lenses.  With  finders  the  trouble  is  sometimes  in  the 
mirror,  which  necessitates  opening  the  finder  and  wiping 
the  mirror  with  a soft  cotton  cloth.  The  brilliant  finders 
of  the  No.  3 A Autographic  Kodaks  can  readily  be  cleaned 
by  lifting  up  front  and  swinging  back  top.  After  cleaning 
as  above  close,  by  simply  snapping  back  into  position. 

35.  (b)  Cleaning  lenses. — Lenses  should  be  frequently 
examined  by  looking  through  them,  and  if  found  to  be 
dirty,  should  be  wiped  both  front  and  back  with  a clean, 
soft  linen  handkerchief.  Large  spots  of  dust  or  dirt  on 
the  lens  will  cause  defects  in  the  picture,  while  if  the  lens 
is  evenly  covered  with  a film  of  dust,  dirt,  or  moisture, 
the  effect  will  be  to  cut  off  a great  deal  of  light  and  make 
the  picture  undertimed. 

36.  (c)  Keep  dust  out  of  the  camera. — Defective  nega- 
tives are  often  caused  by  particles  of  dust  which  have  col- 
lected on  the  inside  of  the  camera  and  settle  upon  the  film  in 
particles  that  produce  small  dark  spots  upon  the  prints. 


MILITAKY  PHOTOGRAPHY. 


21 


III.  THE  3A  GRAFLEX  CAMERA. 

DESCRIPTION. 

37.  Practically  all  that  has  been  said  with  reference  to 
lenses,  stops,  time  of  exposure,  etc.,  in  connection  with  the 
3A  Autographic  camera  is  equally  applicable  to  the  3A 
Graflex  camera. 

38.  This  camera  differs  from  the  former : First,  in  that 
it  is  equipped  with  a finder  which,  when  viewed  from  above, 
shows  an  image  reflected  from  a mirror  set  at  an  angle  of 
45°  to  the  axis  of  the  finder  lens.  The  great  advantage  of 
this  camera  is  that  it  is  focused  when  the  finder  is  focused. 
The  cross  section  of  the  camera  below  shows  the  position 
of  the  mirror  when  set  for  focusing  as  well  as  the  focal 
plane  shutter,  which  operates  just  in  front  of  the  film. 
This  shutter  is  actuated  by  a spring  and  has  different  sized 
slits  so  that  varying  amounts  of  light  reach  the  film, 
depending  upon  the  width  of  the  slit  used. 

39.  The  paths  of  the  rays  A and  B through  the  lens  to 
the  mirror  and  thence  to  the  focusing  screen  are  indicated 
in  Fig.  7.  It  will  be  noted  that  the  image  is  erect.  When 
the  mirror  is  released,  an  instant  before  the  exposure,  the 
rays  pass  directly  through  the  shutter  slit  to  the  film  as  at 
A2  and  B2. 

DIRECTIONS  FOR  OPERATING  THE  3A  GRAFLEX  CAMERA. 

40.  (a)  Loading  the  camera, — The  back  panel  of  cam- 
era is  hinged,  and  may  be  opened  by  releasing  sliding  lock.  ; 
To  load,  the  bracket  carrying  the  spool  at  left  end  of 
camera  is  drawn  forward  until  the  hinged  end  springs 
open.  This  permits  the  spool  to  be  set  in  between  the  cen- 
ters and  the  bracket  pressed  back  into  the  film  pocket, 
securely  holding  the  spool  between  the  centers.  The  black 
paper  is  drawn  across  the  focal  plane  and  threaded  into 
the  receiving  spool,  which  drops  into  position  without  the 
use  of  centers,  journaling  against  the  metal  guide  at  one 
end  and  centering  on  the  winding  key  at  the  other.  When 
the  back  panel  is  closed,  two  light  pressure  bars,  fas- 
tened to  the  face  of  this  panel,  press  the  film  forward  to  a 


22 


MiLllAEY  PHOTOGEAPHY. 


true  focal  plane.  The  film  is  wound  off  until  the  nmnbeP 
of  each  exposure  registers  at  the  small  ruby  window.  Two 
small  pockets  at  either  end  of  camera,  opening  with  spring 
catched  door,  carry  two  extra  rolls  of  film. 


Fig.  7. 


41.  (i)  Focusing. — Adjust  the  focusing  hood  by  re- 
leasing catch  near  center  of  camera.  Eaise  the  cover, 
which  automatically  extends  the  focusing  hood.  Press 
down  the  two  side  arms,  which  will  draw  the  focusing 
hood  taut,  and  hold  it  in  this  position.  Open  front  of  the 
camera  by  pressing  release  button  on  right  upper  forward 


MILITAKY  :photoqraphy.  23 

corner,  draw  out  lens  front  to  desired  position,  and, adjust 
fine  focus  with  rack  and  pinion. 

42.  (c)  Setting  the  mirror. — Press  lever  H down;  until 
it  catches. 

43.  {d)  To  set  shutter  for  instantaneous  worK — Push 
lever  H down  until  it  locks,  which  sets  the  mirror,  - de- 
press disk  D,  which  surrounds  the  shaft  of  lever  H,  and 
revolve  it  until  letter  I stands  directly  opposite  the  white 
mark  on  lever  H,  indicating  instantaneous  exposures. 

44.  {e)  To  set  curtain. — Wind  the  curtain  by  turning 
key  A toward  the  left  until  the  desired  aperture  appears 
at  F.  The  Graflex  curtain  is  made  in  one  long  j)iece,  con- 
taining five  apertures  as  follows : Full  iOpening  for  time 
work,  1-1/2  inch,  3/4  inch,  3/8  inch,  and  1/8  inch  ^fox 
instantaneous  exposures.  Any  of  the  smaller  instanta- 
neous exposing  apertures  may  be  brought  into  position  by 
turning  key  A to  the  left,  running  in  rotation  from  the 
larger  to  the  smaller  apertures  or  the  curtain  may  be 
lowered  from  the  smaller  to  the  larger  apertures  by  press- 
ing on  lever  M directly  above  winding  key.  When  letter  .0 
shows  on  the  aperture  index  at  F the  curtain  is  wide  open, 
and  by  setting  the  curtain  aperture  at  0 and  releasing  the 
mirror  for  instantaneous  work,  a slow  instantaneous  ex- 
posure can  be  made,  giving  practically  a flap  and  drop 
effect. 

45.  (/)  For  time  exposures. — Depress  disk  D and  re- 
volve until  letter  T stands  opposite  the  white  mark  on 
lever  H.  Wind  the  curtain  until  letter  T shows  at  aper- 
ture. Set  the  mirror  in  the  usual  manner.  After  focus- 
ing release  the  mirror,  which  travels  up  out  of  the  cone 
of  light.  Open  the  exposure  by  pressing  lever  M and 
terminate  the  exposure  by  a second  pressure  on  lever  M. 

46.  {g)  For  instantaneous  exposures. — To  make  an  in- 
stantaneous exposure  when  the  object  to  be  photograj^hed 
is  focused  sharply  upon  the  focusing  screen,  a downward 
pressure  on  lever  E,  near  the  front  on  left  hand  side  of 
camera,  releases  the  mirror,  which  travels  up  out  of  the 
cone  of  light,  automatically  releasing  the  shutter,  and  as 


24 


MILITARY  PHOTOGRAPHY. 


the  action  of  these  is  simultaneous  the  object,  although 
moving  broadside  to  the  camera,  can  be  located  perfectly 
in  the  center  of  film. 

47.  (Ji)  Caution. — A safety  lock  prevents  the  curtain 
being  rewound  before  the  mirror  is  set  when  making  in- 
stantaneous exposures.  This  prevents  fogging  the  film, 
making  it  necessary  to  set  the  mirror  before  rewinding 
the  shutter. 

48.  (i)  To  regulate  rate  of  speed. — Turn  milled  head 
to  the  left  until  tension  number  desired  appears  at  Gr.  The 
numbers  run  from  1 to  6,  the  highest  number  indicating 
the  greatest  speed. 

49.  .(i)  To  lower  tension. — Release  spring  by  pushing 
escapement  P back  and  forth,  as  the  tension  may  be  low- 
ered from  the  highest  to  the  lowest  number,  stopping  at 
any  intermediate  number  or  between  numbers. 

50.  The  table  on  back  of  focusing  hood  gives  approxi- 
mate degrees  of  speeds  in  fractional  parts  of  seconds 
obtainable  with  the  tension  numbers  from  1 to  6,  and  the 
various  curtain  apertures.  However,  the  tension  can  be 
set  at  intermediate  points,  giving  a greater  variation  of 
speeds  than  shown  by  this  table. 


MILITAKY  PHOTOGRAPHY 


25 


51.  The  following  tables  will  be  found  useful : 

Table  I. 


When  height  of  image  of  man  or  horse  is  inches  on 
ground  glass,  the  distance  will  be  about,  for  a — Feet. 

5- inch  lens 20 

6- inch  lens 25 

7- inch  lens 30 

8- inch  lens 33 

10-inch  lens 40 

12-inch  lens 50 

14-inch  lens 60 

And  shutter  speed  must  be  at  least — 


When  height  of  image 
of  man  or  horse  is 
f inch  on  ground 
glass  the  distance 
will  be  about,  for 


a — Feet. 

5- inch  lens 40 

6- inch  lens 50 

7- inch  lens 60 

8- inch  lens 66 

10-inch  lens ....  80 

12-inch  lens. . . . 100 
14-inch  lens ....  120 


And  shutter 
speed  must  be  at 
least — 


Subject. 

Figure 
moving 
at  right 
angles  to 
camera. 

At 

45°. 

Figure 

moving 

toward 

camera. 

Figure 
moving 
at  right 
angles  to 
camera. 

At 

45°. 

Figure 

moving 

toward 

camera. 

100-yard  race 

1-655 

1^90 

1-270 

1-330 

1-270 

1-130 

^-mile  race 

1-655 

1-330 

1-215 

1-330 

1-215 

1-105 

i-mile  race 

1-655 

1-330 

1-215 

1-330 

1-215 

1-105 

Swift  skater 

1-1,  000 

1-655 

1-330 

1-490 

1-330 

1-175 

Man  talking  rapidly 

1-160 

1-105 

1-50 

1-75 

1-50 

1-25 

Horse  walking  rapidly 

1-160 

1-105 

1-50 

1-75 

1-50 

1-25 

Bicycle,  ordinary  pace 

1-330 

1-215 

1-105 

1-160 

1-105 

1-50 

Bicycle  racing 

1-655 

1-490 

1-215 

1-330 

1-215 

1-105 

Fast  horse  trotting 

1-1,  000 

1-655 

1-330 

1-490 

1-330 

1-175 

Horse  galloping 

1-1,  200 

1-825 

1-490 

1-655 

1-490 

1-215 

Horse  inmnincr 

1-1.  200 

1-825 

1-490 

1-655 

1-490 

1-215 

Train  or  automobile,  35  miles  an  hour,  distance  100  feet. . 
Train  or  automobile,  60  miles  an  hour,  distance  100  feet. . 

1-330 

1-655 

1-215 

1-490 

1-105 

1-215 

52.  The  following  subjects  need  not  be  specially  rated,  as 
all  of  them  may  be  taken  with  a speed  of  yio  second  or  less. 
Man  walking  slowly,  ^ ; street  scenes,^ ; cattle  grazing, 
boating,  eV;  and  all  slow-moving  subjects. 

9019°— 17 4 


26 


MILITARY  PHOTOGRAPHY. 


53. 


Table  II. — 7 -inch  equivalent  focus  lens. 
DISTANCE  FROM  OBJECT. 


Stop. 

15  feet. 

18  feet. 

24  feet. 

30  feet. 

Depth  of 
field  of 
focus. 

Depth  of 
field  of 
focus. 

Depth  of 
field  of 
focus. 

Depth  of 
field  of 
focus. 

F-5  or  U.  S.  1.56 

F-6.3  or  U.  S.  2.50 

F-8or  U.  S.  4 

Inches. 

31 

40 

51 

71 

Inches. 

45 

58 

74 

103 

1 

Inches. 

80 

102 

132 

189 

1 

Inches. 

126 

161 

211 

311 

F-11  or  U.  S.  8 

IV.  DEVELOPING. 

DEVELOPERS. 

54.  (a)  General. — In  the  field,  where  a dark  room  is 
rarely,  if  ever,  available,  recourse  must  be  had  to  the 
Kodak  film  tank  for  development.  If  used  in  accordance 
with  instructions  and  with  the  prepared  developers  fur- 
bished, it  gives  very  good  results.  There  are  a few  cases, 
however,  where  a skilled  |)hotographer  can  obtain  better 
results  from  hand  development  and  by  mixing  his  own 
developers;  hence  the  following  formulae.  At  least  15 
■different  chemicals  are  good  developing  agents. 

Among  them  are : 


Pyrogallic  acid  (‘‘Pyro”). 
Hydroquinone  or  hydrokinone. 
Metol. 

Amidol. 

Rodinal. 

Glycin. 


Ortol. 

Syntol. 

Eikonogen. 

Diogen. 

Edinol. 

Diamidophenol. 


55.  All  give  much  the  same  final  results,  but  they  vary 
greatly  as  regards  the  manner  and  time  in  which  they 
effect  complete  development. 

56.  Each  constituent  of  a developer  has  its  own  func- 
tion to  perform ; as  follows : 

(1)  The  actual  developing  salt  or  reducing  agent. — 
Pyro,  metol,  hydroquinone,  etc, 


MILITARY  PHOTOGRAPHY. 


27 


(2)  Sodium  sulphite. — In  the  case  of  pyro  it  acts 
partly  as  a preservative,  but  more  particularly  as  an  anti- 
stain. With  some  other  salts  it  also  serves  as  an  ac- 
celerator. 

(3)  The  accelerator. — In  practice  always  an  alkali. 
Sodium  carbonate  is  most  widely  used.  Half  the  quan- 
tity of  potassium  carbonate  may  be  substituted.  As  its 
name  implies,  this  constituent  hastens  development.  An 
excess  of  accelerator  tends  to  cause  fogging. 

(4)  The  restrainer,  bromide  of  potassium. — This  re- 
tards the  action  of  the  developer  and  helps  to  prevent 
fogging.  If  added  at  the  commencement  of  development 
it  will,  within  limits,  correct  overexposure  b}^  holding  back 
the  shadows  and  giving  the  high  lights  and  half  tones  a 
start. 

(5)  The  preservative.— PjTo  stock  developer  requires 
the  addition  of  a preservative,  either  nitric,  citric,  or 
sulphuric  acid,  or  potassium  metabisulphite.  The  last 
named  is  best. 

57.  (&)  Dark-room  developers. — Any  good  developer 
may  be  used  with  any  good  plate  or  film.  Pyro  is  popular, 
as  it  is  cheap,  quick  acting,  and  easily  controlled  by  vary- 
ing the  proportions  of  its  constituents.  The  following  two- 
solution  pyro  developer  is  a good,  clean  working  de- 
veloper : 

PYRO  SODA  DEVELOPER. 

58.  Solution  No.  1.  Label  No.  1 Pyro.” 

Sodium  sulphite Bounces. 

Potassium  metabisulphite 21  drams. 

Pyro 160  grains. 

AVater  to  make  20  oz. 

Dissolve  in  the  order  given. 

59.  Solution  No.  2.  Label  “No.  2 Sod.  Garb.” 

Sodium  carbonate 4oz. 

Water  to  make  20  oz. 

60.  For  use  take  one  part  of  No.  1,  one  part  No.  2,  two 
parts  water.  These  proportions  give  soft  negatives  suit- 
able for  enlarging,  after  from  four  to  six  minutes’  develop- 


28 


MILITARY  PHOTOGRAPHY. 


ment  at  normal  temperatures  (60''  to  65°  F.).  If  more  con- 
trast is  desired  take  equal  parts  of  No.  1,  No.  2,  and  water. 

METOL-HYDROQUINONE  DEVELOPER. 

61.  The  following  is  a nonstaining  developer  suitable 
for  plates  and  bromide  prints : 


62.  A ” solution: 

Metol ^ dram. 

Hydroquinone 1 dram. 

Potassium  metabisulphite | dram. 

Water  to  make  20  oz. 

63.  B ’’  solution: 

Sodium  carbonate 1 oz. 

Sodium  sulphite 1 oz. 

Water  to  make  20  oz. 


For  use  take  equal  parts  of  “A”  and  “ B.” 

64.  (c)  Tank  developers. — In  addition  to  the  prepared 
developers  the  following  formula  has  been  carefully  tested 
and  is  thoroughly  reliable : 

PYRO  TANK  DEVELOPER. 


STOCK  SOLUTION. 

Metol - 60  grains. 

Hydrochinon 240  grains. 

Sodium  sulphite  (dry) 540  grains. 

Sodium  carbonate  (dry) 1,  500  grains. 

Potassium  bromide 30  grains. 

Water 50  ounces. 

FOR  HAND  DEVELOPMENT  USE. 

Stock  solution 4 ounces. 

Dry  pyro . 5 grains. 

Water Bounces. 

FOR  TANK  DEVEOPMENT  USE. 

Stock  solution 10  ounces. 

Dry  Pyro 15  grains. 

Water 40  ounces. 

Develop  10  minutes  at  68°  F. 


GLYCIN  TANK  DEVELOPER. 

STOCK  SOLUTION. 


Hot  water  ( about  200° ) 50  ounces. 

Carbonate  soda  (dry)* 2 ounces. 

Glycin ^ ounce. 

Sulphite  soda  (dry)* jounce. 


Dissolve  in  order  stated. 


* If  crystal  sodas  are  used,  double  the  quantity. 


MILITARY  PHOTOGRAPHY. 


29 


65.  For  lO-minute  development,  use  five  ounces  stock 
solution  to  thirty  ounces  water.  Temperature,  65°.  For 
25-minute  development,  use  two  ounces  stock  solution  to 
thirty-two  ounces  water.  Temperature,  65°. 

THE  FILM  TANK. 

66.  The  Kodak  film  tank  consists  of  a wooden  box,  a 
light-proof  apron,  a ^transferring  reel,”  a metal  ^ Solu- 
tion cup,”  in  which  the  film  is  developed,  and  a hooked  rod 
for  removing  film  from  solution.  There  is  also  a dummy 
film  cartridge  with  which  one  should  experiment  before 
using  an  exposed  cartridge.  The  various  parts  of  the  out- 
fit come  packed  in  the  box  itself. 

67.  {a)  Preparing  the  cartridge, — Film  to  be  used  in 
the  Kodak  film  tank  must  be  fastened  to  the  black  paper  at 
both  ends.  All  films  are  fastened  at  one  end  at  the  factory. 
The  other  end  is  fastened  as  follows.:  Just  before  you  are 
ready  to  develop  (holding  spool  with  the  imprinted  side  of 
the  black  paper  up)  unroll  the  black  paper  carefully  until 
you  uncover  the  piece  of  gummed  paper  which  is  fastened 
to  end  of  film  and  is  to  be  used  as  a means  of  fastening 
film  to  black  paper.  Moisten  the  gummed  side  of  sticker 
evenly  for  about  an  inch  across  the  end  and  stick  it  down 
to  black  paper,  rubbing  thoroughly  to  secure  perfect  ad- 
hesion. Wind  end  of  black  paper  on  spool  again,  and  the 
cartridge  is  ready  to  insert  in  machine. 

68.  (&)  Setting  up  the  film  tank. — Take  everything  out 
of  the  box.  Take  the  apron  and  transferring  reel  out  of 
solution  cup. 

69.  The  axles  marked  C and  D in  the  cut  are  to  be  in- 
serted in  the  holes  in  the  front  of  box.  The  front  will  be 
toward  you  when  the  spool  carrier  in  end  of  box  is  at  your 
right.  These  axles  are  interchangeable.  The  axle  C must 
be  pushed  through  the  hollow  spindle  which  will  be  found 
loose  in  the  box.  This  spindle  has  a lug  at  each  end  to 
which  the  hooks  of  the  apron  are  to  be  attached. 

70.  The  axle  J)  must  be  pushed  through  the  hollow  rod 
of  the  transferring  reel  to  hold  reel  in  position  as  indicated 
in  the  illustration.  The  fianges  at  each  end  of  the  trans- 
ferring reel  are  marked  Y in  the  illustration.  Both  axles 
C and  D must  be  pushed  clear  through  into  the  holes  on 
the  opposite  side  of  the  box. 


30 


MILITARY  PHOTOGRAPHY. 


71.  Attach  one  end  of  the  apron  to  spindle,  through 
which  axle  C passes,  by  means  of  the  metal  hooks  which 
are  to  be  engaged  with  the  lugs  on  the  spindle.  The  cor- 
rugated side  of  the  rubber  bands  is  to  be  beneath  the  apron 
when  it  is  attached.  Turn  to  left  on  axle  C and  wind  en- 
tire apron  on  to  axle,  maintaining  a slight  tension  on  apron 
in  so  doing  by  resting  one  hand  on  it. 

72.  (c)  Operating  the  film  tank, — Insert  film  cartridge 
in  spool  carrier,  and  close  up  the  movable  arm  tight  against 
end  of  spool ; have  the  black  paper  lead  from  the  top. 


i 


Fig.  8. 

73.  Thread  the  paper  underneath  wire  guard  on  trans- 
ferring reel,  through  which  axle  D passes,  and  turn  axle 
slowly  to  right  until  the  word  ‘^stop”  appears  on  black 
paper. 

74.  Now  hook  apron  to  lugs  on  transferring  reel  in 
precisely  the  same  manner  that  you  hooked  the  opposite 
end  to  lugs  on  the  spindle,  except  that  axle  D turns  to  the 
right. 

75.  Turn  handle  half  a revolution  so  that  apron  be- 
comes firmly  attached  and  put  on  cover  of  box.  Turn  axle 
D slowly  and  steadily  until  black  paper,  film  and  apron 
are  rolled  up  together  on  reel.  As  soon  as  this  is  com- 
peted the  handle  will  turn  very  freely. 

76.  Prepare  developer  as  described  below. 

77.  Now  remove  cover  from  box  and  draw  out  axle  D, 
holding  apron  and  black  paper  with  other  hand  to  keep 
end  of  apron  from  loosening. 


MILITARY  PHOTOGRAPHY. 


31 


78.  Remove  entire  transferring  reel  (now  containing 
apron,  black  paper,  and  film),  which  is  freed  by  pulling 
out  axle  D,  and  insert  immediately  in  the  previously  pre- 
pared developer.  In  removing  reel  do  not  squeeze  the 
apron,  but  hold  it  loosely  or  slip  a rubber  band  about  it 
to  keep  from  unrolling. 

78.  {d)  Using  the  solution  cup. — Having  filled  solution 
cup  as  directed  hereafter,  lower  transferring  reel  into  cup, 
with  the  end  containing  crossbar  up.  Let  reel  slide  down 
slowly.  The  operation  of  removing  reel  from  box  can  be 
done  in  the  light  of  an  ordinary  room,  but  for  safety  it 
is  well  that  the  light  should  not  be  too  bright.  The  total 
length  of  time  for  development  is  20  minutes.  Then  place 
the  cover  on  the  cup,  putting  lugs  on  cover  into  the 
grooves,  and  tighten  cover  down  by  turning  it  to  right. 
Now  turn  the  entire  cup  end  for  end  and  place  in  a tray  or 
saucer  to  catch  any  slight  leak  from  the  cup. 

79.  At  the  end  of  3 minutes  again  reverse  the  cup,  and 
thereafter  reverse  every  3 minutes  until  the  time  of  devel- 
opment (20  minutes)  has  elapsed. 

80.  Turning  the  solution  cup  in  this  manner  allows 
the  developer  to  act  evenly  and  adds  brilliancy  and  snap 
to  the  negatives. 

81.  The  wire  hook  is  to  be  used  for  lifting  the  reel  out 
of  the  cup.  Hook  on  to  the  crossbar  in  one  end  of  reel. 

82.  Immediately  after  lowering  reel  into  solution  cup 
catch  it  with  wire  hook  and  move  slowly  up  and  down  two 
or  three  times,  taking  care,  however,  not  to  raise  any  part 
of  reel  above  the  surface  of  solution.  This  is  to  expel  air 
bubbles. 

83.  When  development  is  completed  pour  out  devel- 
oper and  fill  cup  with  clear,  cold  water  and  pour  off, 
repeating  this  operation  three  times  to  wash  the  film. 
Then  remove  transferring  reel ; separate  film  from  black 
paper  and  place  immediately  in  the  fixing  bath,  which 
should  be  in  readiness,  prepared  in  accordance  with  di- 
rections. (See  p.  47.) 

84.  The  film  may  be  separated  from  black  paper  in 
light  of  an  ordinary  room  if  the  developer  is  thoroughly 
washed  out. 


32 


MILITARY  PHOTOGRAPHY, 


85.  The  operation  of  separating  film  and  black  paper 
should  be  done  over  a bowl  or  bathtub  or  sink. 

86.  When  the*  black  paper  does  not  free  itself  readily 
from  back  of  film  split  the  paper  where  possible ; this  will 
remove  the  hard  outer  surface  of  the  paper ; the  remain- 
ing portion  will  soon  become  ‘^oaked  and  can  then  be  re- 
moved easily  by  rubbing  gently,  while  immersed,  with  the 
ball  of  the  finger.  This  adhering  of  the  black  paper  to 
the  film  is  almost  invariably  caused  by  the  use  of  a too 
warm  developer. 

87.  After  developing  a roll  of  film  the  apron  must  be 
wiped  dry  before  developing  another  roll.  The  apron  will 
dry  almost  instantly  if  immersed  for  a moment  in  very 
hot  water. 

88.  Keep  apron  wound  on  axle  D when  not  in  use. 
Never  leave  apron  soaking  in  water. 

89.  {e)  Preparing  the  developer. — The  kodak  tank  de- 
veloper powders  are  prepared  especially  for  use  with  East- 
man films  and  the  kodak  film  tank. 

90.  Put  4 or  5 ounces  of  lukewarm  water  into  the  solu- 
tion cup,  and  dissolve  in  it  the  contents  of  the  large  pack- 
age. Fill  the  cup  with  cold  water  to  the  embossed  ring — 
not  to  the  top.  Now  dissolve  the  contents  of  the  small 
package  in  this  solution  and  the  developer  will  be  ready. 
The  temperature  of  the  developer  should  be  65°  F. 

91.  If  some  of  the  contents  of  the  small  package  stick 
to  the  paper,  dip  the  paper  into  the  solution  to  remove. 

92.  The  developer  must  always  be  mixed  fresh  and  used 
for  only  one  roll  of  film. 

93.  (/)  Short  development. — If  it  is  desired  to  shorten 
the  length  of  development,  equally  good  results  may  be  ob- 
tained by  using  two  pairs  of  the  powders  and  developing 
for  10  minutes. 

94.  (g)  Developer  formulas. — Those  who  wish  to  prepare 
their  own  developer  may  do  so,  but  care  must  be  exercised 
in  securing  absolutely  pure  chemicals  and  correct  weights. 

FOR  20-MINUTE  DEVELOPMENT — 3J-INCH  TANK. 

22  grains  pyro. 

66  grains  sulphite  of  soda,  desiccated.^ 

44  grains  carbonate  of  soda,  desiccated.^ 


1 If  crystals  are  us(h1,  double  the  quantity. 


MILITARY  PHOTOGRAPHY. 


. 33 


95.  Dissolve  the  chemicals,  in  order  named,  in  five  or’ 
six  ounces  of  lukewarm  water,  then  add  cold  water  to  fill 
tank  to  embossed  ring. 

FOR  10-MINUTE  DEVELOPMENT 3J-INCH  TANK. 

44  grains  pyro. 

132  grains  sulphite  of  soda,  desiccated/ 

88  grains  carbonate  of  soda,  desiccated.^ 

I 

96.  Dissolve  the  chemicals,  in  order  named,  in  five'  or 
six  ounces  of  lukewarm  water,  then  add  cold  water  to  fill 
tank  to  embossed  ring. 

97.  (li)  Time  and  temperature  for  tank  development. — 
It  sometimes  happens  that  the  amateur  is  not  able  to 
obtain  or  maintain  the  standard  or  normal  temperature 
of  65°  P.  when  using  the  Kodak  tank  and  the  Kodak  tank 
developer  powders.  In  such  cases  the  following  table  will 
be  found  of  value : 


Tempera- 

ture. 

Time-one 

powder. 

Time-two 

powders. 

Degrees. 

Minutes. 

Minutes. 

70 

15 

8 

69 

16 

68 

17 

9 

67 

18 

66 

19 

2 65 

2 20 

2 10 

64 

21 

63 

22 

62 

23 

11 

61 

24 

60 

25 

59 

26 

12 

58 

27 

57 

28 

56 

29 

13 

55 

30 

54 

31 

53 

32 

14 

52 

33 

51 

34 

50 

35 

15 

49 

36 

48 

37 

47 

38 

16 

46 

39 

45 

40 

17 

1 Normal. 

2 If  crystals  are  used,  double  the  quantity. 


9019°— 17 5 


34  , 


MILITARY  PHOTOGRAPHY. 


98.  Temperature  of  developer  must  not  exceed  70°  F., 
as  above  that  point  there  is  danger  of  the  film  frilling; 
45°  P.  is  the  lowest  temperature  at  which  the  developing 
powders  can  be  dissolved,  and  even  at  this  temperature 
the  powder  must  be  finely  crushed  and  added  slowly  to 
the  water. 

99.  It  is  best  to  use  the  normal  temperature  (65°) 
when  possible,  as  the  use  of  a developer  that  is  colder  than 
normal  has  a slight  tendency  to  increase  the  contrast  in  a 
negative,  while  the  use  of  a developer  warmer  than  normal 
slightly  flattens  the  resulting  negatives. 

100.  (i)  Sea  water, — It  has  been  fully  demonstrated 
that  sea  water  may  safely  be  used  in  compounding  the 
developer  and  for  all  the  processes  of  tank  development, 
provided  only  that  the  final  rinsing  is  in  clean,  fresh 
water. 

101.  (j)  Troubles  with  negatives. — Fog  is  caused  (1) 
by  admission  of  light  during  development;  (2)  leakage 
in  the  camera  or  plate  holder;  (3)  reflection  of  light  from 
the  inside  of  the  camera;  (4)  dust  or  dew  on  the  lens;  (5) 
overdevelopment.  The  third  cause  is  the  result  of  using 
a lens  which  more  than  covers  the  plate.  It  is  obviated 
by  a lens  hood  or  by  a blackened  card  interposed  between 
lens  and  plate  with  an  opening  of  such  a size  as  to  pass 
only  light  which  will  reach  the  plate  direct  from  the  lens. 
Fog  due  to  overexposure  and  overdevelopment  can  be 
remedied  by  reduction  if  not  too  pronounced. 

102.  Light  patches, — Caused  by  imperfect  flooding,  so 
that  the  developer  does  not  take  hold  of  all  the  film  at  once. 

103.  Dark  patches. — May  be  due  to  emanations  from 
the  camera  if  the  films  have  been  kept  in  it  for  a long  time. 
If  a partly  dried  negative  is  warmed  to  complete  the  dry- 
ing there  may  also  be  a darkening  of  the  parts  thus  dried. 

104.  Bound  transparent  spots. — Caused  by  air  bells  on 
the  film  which  prevented  development  of  the  parts  so  cov- 
ered. If  the  surface  of  the  film  is  wiped  over  with  a pad 
of  wet  cotton  wool  immediately  after  flooding,  any  air  bells 
present  will  be  removed. 


MILITARY  PHOTOGRAPHY. 


35 


105.  Pinholes. — Due  to  dust  on  the  film  during  ex- 
posure. This  is  a very  common  trouble.  Plate  carriers 
and  camera  should  be  dusted  occasionally,  especially  in 
dry  weather. 

106.  Mottling  of  film. — Due  to  not  moving  the  film  dur- 
ing development. 

107.  Black  spots. — Due  (a)  to  metallic  rust  in  the  water. 
Always  let  some  water  run  to  waste  before  using  the  tap 
for  the  first  time  in  a day;  (b)  to  pyro  dust  settling  on  the 
plate.  Overworked  pyro  developer  is  liable  to  deposit  on 
a negative  and  produce  black  spots. 

V.  THE  FIXING  BATH. 

108.  Provide  a box  of  Kodak  acid  fixing  powder,  which 
should  be  prepared  as  follows : Remove  the  cover  from  the 
box  and  pour  into  the  cover. enough  of  the  fixing  powder 
to  fill  the  cover  level  full.  Put  this  into  a tray  or  wash- 
bowl and  add  8 ounces  of  cold  water.  When  the  powder  is 
thoroughly  dissolved,  add  to  the  solution  as  much  of  the 
acidifier,  which  you  will  find  in  a small  box,  inside  the  large 
one,  as  will  fill  the  cover  of  the  small  box  level  full.  As 
soon  as  this  has  dissolved  the  fixing  bath  is  ready  for  use. 
Any  quantity  of  the  bath  may  be  prepared  in  the  above 
proportions. 

109.  Pass  the  film,  face  down  (the  face  is  the  dull  side), 
through  the  fixing  solution,  holding  one  end  in  each  hand. 
Do  this  three  or  four  times  and  then  place  one  end  of  the 
film  in  the  tray,  still  face  down,  and  lower  the  strip  into 
the  solution  in  folds.  Gently  press  the  film  where  the  folds 
occur,  not  tightly  enough  to  crack  it,  down  into  the  solu- 
tion a few  times  during  the  course  of  fixing.  This  insures 
the  fixing  solution  reaching  every  part  of  the  film.  Allow 
the  film  to  remain  in  the  solution  two  or  three  minutes 
after  it  has  cleared  or  the  milky  appearance  has  disap- 
peared. Then  remove  for  washing. 


36  MILITARY  PHOTOGRAPHY. 

110.  Eastman  N.  C.  film  must  always  be  fixed  in  an  acid 
bath.  If  Kodak  acid  fixing  powders  can  not  be  obatined, 
the  following  formula  may  be  used  if  desired : 

Water  16  ounces. 

Hypo-sulphite  of  soda 4 ounces. 

Sulphite  of  soda  (desiccated) 80  grains. 

When  fully  dissolved,  add  the  following  hardener: 


Powdered  alum | ounce. 

Citric  acid , i ounce. 


111.  This  bath  may  be  made  up  at  any  time  in  advance 
and  be  used  so  long  as  it  retains  its  strength,  or  is  not 
sufficiently  discolored  by  developer  carried  into  it  as  to 
stain  the  negatives. 

VI.  WASHING. 

112.  There  are  several  ways  of  washing  film.  It  may 
be  placed  in  a washbowl  of  cold  water  and  left  to  soak 
for  five  minutes  each  in  five  changes  of  cold  water,  mov- 
ing it  about  occasionally  to  insure  this  water  acting  evenly 
upon  it,  or  it  may  be  given,  say,  two  changes  as  above 
and  then  left  for  an  hour  in  a bowl  with  a very  gentle 
stream  of  water  running  in  and  out. 

VII.  DRYING  FILM  NEGATIVES. 

113.  When  thoroughly  washed,  snap  a clip  on  each  end 
of  the  strip  and  hang  it  up  to  dry,  or  pin  it  up.  Be  sure, 
however,  that  it  swings  clear  of  the  wall,  so  that  there 
will  be  no  possibility  of  either  side  of  the  film  coming  in 
contact  with  the  latter. 

114.  If  the  film  has  been  cut  up,  pin  by  one  corner  to 
the  edge  of  a shelf  or  hang  the  negatives  on  a stretched 
string  by  means  of  a bent  pin,  running  the  pin  through 
the  corner  of  film  to  the  head,  then  hooking  it  over  the 
string  . 

VIII.  AFTER  TREATMENT  OF  NEGATIVES. 

A.  OVER-DEVELOPMENT. 

115.  Caused  by  leaving  the  negative  too  long  in  the  de- 
veloper, or  by  using  develo]ier  too  warm.  In  this  case 
the  negative  is  very  strong  and  intense  by  transmitted 


MILITARY  PHOTOGRAPHY. 


37 


light  and  requires  a very  long  time  to  print.  The  remedy 
is  to  reduce  by  the  following  method : 

116.  First  soak  negative  20  minutes  in  water,  then  im- 
merse in : 

. KEDUCER. 


Water 6 ounces. 

Hyposulphite  soda i ounce. 


Ferricyanide  potassium  (saturated  solution).  Poison 20  drops. 

117.  Rock  tray  gently  back  and  forth  until  negative  has 
been  reduced  to  the  desired  density,  then  wash  10  minutes 
in  running  water  or  in  four  changes  of  water. 

118.  Negatives  may  be  reduced  locally -by  applying  the 
above  solution  to  the  dense  parts  with  a cameFs-hair 
brush,  rinsing  off  the  reducer  with  clear  water  frequently 
to  prevent  its  running  onto  the  parts  of  the  negative  that 
do  not  require  reducing. 

119.  Should  any  yellowness  or  staining  appear  in  the 
reduced  negative,  it  may  be  removed  by  replacing  same  in 
the  acid  fixing  bath  for  a few  minutes. 

B.  UNDER  DEVELOPMENT. 

120.  Caused  by  removal  from  the  developer  too  soon. 

121.  An  underdeveloped  negative  differs  from  an  un- 
derexposed one,  in  that  it  is  apt  to  be  thin  and  full  of 
detail,  instead  of  harsh  and  lacking  in  detail.  If  the  de- 
velopment is  carried  on  as  before  directed,  this  defect  is 
not  liable  to  occur. 

122.  If  a mistake  has  been  made  in  developing  and  the 
negative  does  not  appear  strong  enough  (this  can  be 
judged  only  by  experience),  the  negative  can  be  im- 
proved by  intensification  as  follows : 

123.  After  fixing  and  thorough  washing,  lay  the  film, 
while  wet,  in  an  empty  tray  and  pour  over  it  sufficient 
intensifier  to  fully  cover  it ; allow  it  to  act  until  the  film 
is  all  of  one  even  color  and  then  pour  the  intensifier  back 
into  the  bottle  and  wash  the  film  in  four  or  five  changes 
of  water  for  15  minutes. 

124.  Intensifier  may  be  purchased  already  prepared 
or  the  amateur  may  put  it  up  himself,  using  the  following 
formula. 


38 


MILTTATiY  PHOTOGRAPHY. 


INTENSIFIER. 

No.  1,  75  gr.  bichloride  of  mercury  (corrosive  sub- 


limate), poison 5 oz.  water. 

No.  2,  112  gr.  iodide  of  potassium 2J  oz.  water. 

No.  3,  150  gr.  hyposulphite  of  soda 2^  oz.  water. 


125.  Dissolve  separately  and  combine  isTo.  1 with  No.  2, 
and  the  resulting  mixture  with  No.  3. 

IX.  IN  THE  TROPICS— PRECAUTIONS. 

126.  Travelers  in  tropical  or  semitropical  countries  will 
find  their  films  ruined  by  the  excessive  dampness  unless 
they  make  proper  provision  against  it. 

127.  The  only  safe  method  is  to  put  up  the  film  in  her- 
metically sealed  tin  cans  (one  spool  to  a can)  and  leave 
them  in  the  cans  until  ready  for  use.  After  exposure  they 
must  be  promptly  developed.  There  is  no  use  in  returning 
them  to  the  can  after  exposure,  as  they  are  likely  to  have 
absorbed  sufficient  moisture  during  exposure  to  ruin  them 
unless  they  are  promptly  developed. 

128.  Kodak  cartridges  will  be  packed  in  sealed  tubes 
on  request,  at  5 cents  each. 

X.  PRINTING. 

A.  ARGO  PAPER. 

LIGHT. 

129.  The  paper  can  be  safely  handled  8 feet  from  the 
source  of  light,  which  may  be  Welsbach  gas  light,  covered 
with  post  office  paper;  incandescent  light,  ordinary  gas 
light,  kerosene  lamp,  or  very  subdued  daylight. 

PRINTING. 

130.  Place  paper  in  an  ordinary  printing  frame,  the 
same  as  with  printing-out  paper.  After  the  paper  is  in 
perfect  contact  with  negative,  expose  by  holding  tlie  print- 
ing frame  close  to  gas,  lamp,  or  incandescent  light,  or  to 
subdued  daylight.  Artificial  light  is  recommended  in 
preference  to  daylight,  because  of  uniformity,  and  it  being 
in  consequence  easier  to  judge  the  proper  length  of  time  to 
expose. 


MILITARY  PHOTOGRAPHY. 


39 


TIMING  THE  EXPOSURE. 

131.  Time  necessary  for  exposing  is  regulated  by  den- 
sity of  negative  and  strength  of  light.  It  takes  about  the 
same  time  with  an  ordinary  gas  burner  as  with  an  incan- 
descent light;  a Welsbach  gas  light  requires  only  about 
one-half  as  much  time  as  the  ordinary  gas  burner,  and 
with  a kerosene  lamp  of  moderate  strength,  at  least  three 
times  the  exposure  necessary  with  a common' gas  burner  is 
required.  If  daylight  is  used,  care  must  be  taken  not  to 
overexpose,  as  its  action  on  the  paper  is  much  more  rapid 
than  the  strongest  artificial  light.  Where  artificial  light 
is  used,  keep  printing  frame  in  motion  during  exposure. 
To  secure  the  correct  time  of  exposure,  a trial  should  be 
made  at  a given  distance  from  the  light  used,  and  if  subse- 
quent exposures  are  allowed  the  same  time  at  the  same 
distance  from  the  light,  the  results  can  not  fail  to  be  abso- 
lutely uniform.  With  negatives  of  average  density,  1 foot 
from  an  ordinary  gas  burner,  from  one  fo  two  minutes’ 
exposure  is  required. 

TO  DEVELOP. 

132.  After  exposing,  immerse  print  in  developing  solu- 
tion made  as  per  formula.  The  print  will  develop  rap- 
idly, and  should  be  closely  watched.  As  soon  as  desired 
depth  is  obtained,  remove  immediately  to  a tray  of  clean 
water,  preferably  acidified  with  acetic  acid  (about  two 
ounces  to  a gallon  of  water),  in  order  to  stop  development 
and  neutralize  the  alkali  adhering  to  the  print;  from 
there  direct  to  fixing  solution,  mixed  as  given  below : 

METOL  QUINOL  DEVELOPER. 


Water 10  ounces. 

Metol 7 grains. 

Sodium  sulphite  (dry  powder) 120  grains. 

Or  crystals,  double  the  quantity. 

Hydroquinone 80  grains. 

Sodium  carbonate  (dry  powder) 200  grains. 

Or  crystals,  double  the  quantity. 


133.  When  mixed,  add  to  the  above  15  to  25  drops  of  a 
bromide  potassium  solution  composed  of  : 


Bromide  of  potassium 1 ounce. 

Water 10  ounces. 


40  MILITARY  PHOTOGRAPHY. 

AMIDOL  DEVELOPEK. 

Amidol 20  grains. 

Sulphite  soda  (crystals) 160 grains. 

Or  dry,  in  the  form  of  powder,  half  the  amount. 

Water 8 ounces. 

134.  When  mixed,  add  to  above  5 to  10  drops  of  a 
bromide  of  potassium  solution  composed  of : 

Bromide  of  potassium 1 ounce. 

Water 10  ounces. 

METOL  HYDRO  ANTIFRICTION  DEVELOPER. 

Water 16  ounces. 

Hydroquinone__^ 80  grains. 

Metol 24  grains. 

‘ Argo  soda 480  grains. 

METOL  HYDROEDINOL  ANTIFRICTION  DEVELOPER. 

(For  very  black  tones.) 

Water 32  ounces. 

Hydroquinone 30  grains. 

Metol 90  grains. 

Edinol 90  grains. 

Argo  soda 2 ounces. 

DEFENDOL  DEVELOPER. 

Water 8 ounces. 

Defendol 60  grains. 

Carbonate  soda  (dry  powder) 240 grains. 

Or  crystals,  double  the  quantity. 

135.  Always  dissolve  defendol  before  adding  carbonate 
soda. 

136.  When  mixed,  add  to  the  above  5 drops  bromide 
potassium  solution  composed  of : 

Bromide  of  potassium 1 ounce. 

Water 10  ounces. 

137.  For  Argo  gloss  and  Argo  luster  the  makers  of  Argo 
paper  recommend  antifriction  developer.  For  all  other 
surfaces,  on  account  of  simplicity  of  manipulation,  they 
recommend  defendol. 

138.  Always  keep  developer  ice  cold,  as  it  improves  the 
tone,  and  the  image  is  much  easier  to  control. 

FIXING  BATH  FORMULA. 


Water. 

Hypo_. 


64  ounces. 
16  ounces. 


MILITARY  PHOTOGRAPHY.  41 

Dissolve,  then  add  the  following  hardening  solution: 

Water 5 ounces. 

Sulphite  soda  crystals 1 ounce. 

Or  powdered  dry,  half  as  much. 

Commercial  acetic  acid 3 ounces. 

Powdered  alum 1 ounce. 

This  is  ready  for  use  as  soon  as  mixed. 


FIXING. 

139.  Allow  prints  to  remain  in  fixing  solution  10  to  20 
minutes ; then  they  should  be  removed  to  a tray  containing 
clear  water. 


WASHING. 

140.  Wash  1 hour  in  running  water,  or  in  10  or  12 
changes  of  clear  water,  allowing  prints  to  soak  2 to  3 min- 
utes in  each  change. 


MOUNTING. 

141.  After  prints  are  washed,  they  may  be  mounted  on 
cardboard  by  following  method : Lay  prints  face  down  on 
glass,  one  on  top  of  the  other ; squeeze  out  surplus  water ; 
apply  a thick  starch  paste  to  the  back  of  topmost  print; 
lay  print  on  card  and  rub  down.  Sponge  face  of  print 
with  a clean,  damp  sponge  to  remove  foreign  substances 
and  surplus  paste  from  edges.  Prints  can  then  be  put 
between  blotters,  or  laid  out  on  a table,  face  upward,  to  dry. 

NOTES. 

142.  Prints  must  be  rinsed  a few  seconds  between  the 
developing  and  fixing  solutions  in  order  to  keep  the  hypo 
free  from  alkali.  This  is  also  an  effective  method  of  pre- 
venting yellow  stains. 

143.  Developer  may  be  used  several  times,  but  fresh 
developer  is  always  recommended. 

144.  If  print  is  overtimed,  the  image  will  flash  up 
quickly  in  developer,  high  lights  will  be  printed  through, 
and  there  will  be  a general  weak,  muddy  effect.  If  under- 
timed, the  resulting  print  will  be  harsh  and  contrasty. 


42 


MILITARY  PHOTOGRAPHY. 


145.  Underexposed  prints,  which  have  of  necessity  been 
forced  in  development,  will  not  have  clear  whites,  hut 
such  prints  may  be  somewhat  improved  by  leaving  in  fix- 
ing bath  from  30  to  60  minutes. 

146.  Blue  tones  or  blue-black  tones  are  obtained  by 
using  only  sufficient  bromide  of  potassium  to  clear  the 
high  lights. 

147.  Fog  is  caused  by  having  the  light  too  strong,  by 
exposing  for  too  long  a time  to  the  rays  of  a supposed  safe 
light,  or  by  using  too  little  bromide  of  potassium.  The 
amount  of  bromide  of  potassium  recommended  in  formula 
is  as  little  as  should  be  used,  but  owing  to  varied  conditions 
an  increased  amount  may  at  times  be  found  necessary. 
Except  when  printing,  the  paper  should  be  handled  at 
least  8 feet  away  from  the  source  of  light,  and  always  be 
kept  in  package,  where  it  is  protected. 

B.  VELOX  PAPERS. 


148.  Arrange  three  traj^s  before  you  in  this  order : 


2 ozs.  nepera 

4 ozs.  liypo. 

solution. 

Clean  water. 

16  ozs.  water. 

4 ozs.  water. 

o 

H 

1 oz.  hardener. 

1 

2 

3 

149.  Do  not  be  too  sparing  of  the  amount  of  the  solu- 
tions used,  especially  of  your  fixing  bath  (tray  No.  3)  ; 
if  making  three  or  four  dozen  prints  (4  by  5)  use  a full 
pint ; and  do  not  keep  it  after  using,  as  a fresh  bath  will 
give  best  results. 

150.  Proper  temperature  is  important  and  for  best  re- 
sults the  developer  should  be  70°  P.  and  the  fixing  bath 
and  wash  water  50°  F.  If  the  developer  exceeds  70°  the 
prints  are  liable  to  fog  and  the  emulsion  soften.  If  too 
cold,  chemical  action  is  retarded,  resulting  in  flat,  weak 
prints. 

PRINTING. 

151.  Place  the  sensitized  side  of  the  sheet  of  Velox 
against  the  film  side  of  the  negative;  the  paper  curls 


MILITARY  rHOTOGRAPHY. 


43 


slightly,'  the  sensitive  side  being  concave.  An  absolute 
test  is  to  bite  the  corner  of  the  sheet ; the  sensitive  side  will 
adhere  to  the  teeth. 

152.  Place  the  printing  frame  the  correct  distance  from 
the  artificial  light  used,  holding  the  frame  away  from 
the  burner  a distance  equal  to  the  diagonal  of  the  nega- 
tive. A few  seconds’  exposure  will  be  required  when 
printing  an  average  negative  on  Special  Yelox.  Regular 
Velox  needs  from  four  to  five  times  as  much  exposure  as 
Special,  if  in  using  both  grades  the  printing  frame  is  held 
at  the  same  distance  from  the  light. 

153.  The  dry  print  should  be  immersed  face  up  in  the 
developer  and  quickly  and  evenly  covered  with  the  solu- 
tion. Regular  Yelox  should  be  developed  15  to  20  sec- 
onds ; Special,  about  30  seconds. 

154.  As  soon  as  the  image  has  reached  the  desired  depth 
remove  from  the  developer  to  the  tray  (Yo.  2)  and  rinse 
for  a moment,  turning  the  print  several  times,  then  place 
it  in  the  acid  fixing  bath  tray  (Yo.  3),  keeping  the  print 
moving  for  a few  seconds,  the  same  as  was  done  when 
rinsing,  so  as  to  give  even  and  thorough  fixing,  preventing 
stains  and  other  troubles.  Leave  the  print  in  this  solu- 
tion until  thoroughly  fixed ; this  will  take  about  15  min- 
utes. When  fixed,  remove  from  the  fixing  bath  and  wash 
thoroughly  for  about  an  hour  in  running  water,  then  dry. 
After  drying,  prints  may  be  trimmed  and  mounted. 

155.  Care  must  be  taken  to  prevent  the  Hypo  in  any 
way  getting  into  the  tray  containing  the  developer.  Have 
a clean  towel  when  beginning  the  work  and  wipe  your 
hands  each  time  after  you  have  handled  prints  in  Hypo 
solution. 

M-Q  DEVELOPER. 

(Dissolve  chemicals  in  the  order  named.) 

Metric  system. 

Water 10  ounces=300  c.  c. 

IMetol 7 grains=i  gram. 

Hydroquinone 30  grains— 2 grams. 

Sulphite  soda  (desiccated) 110  grains=7  grams. 

Carbonate  soda  (desiccated) 200  grains=13  grams. 

10  per  cent  solution  bromide  potassium_____  40  drops=40  drops. 


44 


MILITARY  PHOTOGRAPHY. 


156.  This  solution  will  keep  indefinitely  if  placed  in 
bottles  filled  to  the  neck  and  tightly  corked.  It  should  be 
used  full  strength. 

157.  To  secure  permanency  prints  must  be  fixed  in  a 
fresh,  acid  fixing  bath.  When  hypo  is  first  dissolved  in 
water,  the  temperature  of  the  solution  is  materially  re- 
duced. It  is  important  that  the  temperature  of  a fixing 
bath  should  be  maintained  as  near  to  50""  F.  as  possible. 
Probably  more  prints  change  color  from  insufficient  fixing 
than  lack  of  washing,  so  these  points  should  be  given  atten- 
tion. Have  plenty  of  solution  strong  enough  to  thor- 
oughly fix  prints  in  at  least  15  minutes.  Always  use  the 
acid  hardener  in  the  bath,  as  it  will  overcome  the  tendency 
of  the  fixing  bath  to  cause  blisters  and  stains. 

158.  Formula  for  preparing  the  acid  hypo  fixing  bath 


is  as  follows : 

Water 64  ounces. 

Hypo-sulphite  of  soda  (crystal  or  granulated) 16  ounces. 


159.  When  thoroughly  dissolved,  add  the  following 
hardening  solution,  dissolving  the  chemicals  separately 


and  in  the  order  named : 

Water 5 ounces. 

Sulphite  of  soda  ( desiccated ) i ounce. 

Acetic  acid  No.  8 (containing  25  per  cent  pure  acid) — 3 ounces. 
Powdered  alum 1 ounce. 


160.  This  solution  will  keep,  and  1 pint  of  it  will  fix 
at  least  one-half  gross  of  4 by  5 prints.  If  sulphite  and 
carbonate  of  soda  in  crystal  form  are  substituted  for  desic- 
cated, double  the  quantities  mentioned  should  be  used. 

NOTES  ON  WASHING. 

161.  The  finished  prints  must  be  entirely  free  from 
Hypo.  To  wash  a batch  of  one  hundred  4 by  5 prints, 
using  two  trays  of  suitable  size  and  transferring  each 
print  separately  from  one  tray  to  the  other,  changing  the 
water  at  least  12  times,  will  take  a full  hour  for  the 
process.  In  running  water  where  the  prints  can  be  kept 
constantly  moving  so  that  each  individual  print  has  a 
thorough  washing,  from  one-half  to  one  hour,  according 


MILITARY  PHOTOGRAPHY. 


45 


to  the  number  of  prints,  will  be  required.  Prints  do  not 
wash  if  piled  in  a bunch  in  a tray  and  the  water  simply 
runs  in  at  one  end  of  the  tray  and  out  of  the  other.  In 
some  localities  where  there  is  an  excessive  amount  of  iron 
or  impurity  in  water  the  whites  in  the  prints  may  have  a 
slight  yellowish  tone.  Prints  should  not  be  allowed  to 
wash  any  longer  than  is  necessary  to  completely  free  them 
from  H}q)0.  The  temperature  of  the  water  in  winter 
should  be  kept  as  uniform  as  possible,  as  ice-cold  water 
will  cause  blistering.  When  running  water  is  used  for 
washing,  the  stream  should  not  be  allowed  to  fall  directly 
on  the  prints,  as  it  will  cause  breaks  in  the  fiber  of  the 
paper,  producing  blisters.  Place  a tumbler  or  graduate 
in  the  washing  tray  and  allow  the  water  to  run  into  it  and 
overflow  into  the  tray.  To  determine  when  the  print  is 
thoroughly  free  from  Hypo,  the  following  test  formula 
may  be  successfully  employed : 


Permanganate  of  potash 8 grains. 

Caustic  soda 7 grains. 

Water  (distilled) 8 ounces. 


162.  Fill  a glass  with  pure  water  to  which  you  have 
added  three  or  four  drops  of  the  potash  solution.  Then 
take  a couple  of  prints  from  the  wash  water  and  allow  the 
water  from  the  prints  to  drip  into  the  glass.  If  Hypo  is 
present,  the  violet  color  of  the  water  in  the  glass  will 
change  to  a slight  greenish  tint.  In  such  case  return 
prints  to  the  wash  water,  to  remain  until  similar  tests  show 
that  the  Hypo  has  been  entirely  eliminated. 

DRYING. 

163.  After  prints  have  been  thoroughly  washed,  remove 
from  the  wash  water  and  place  on  a clean  glass  in  a pile, 
face  down,  and  press  out  superfluous  water.  Then  lay  out 
separately,  face  down,  on  cheesecloth  stretchers.  These 
may  be  constructed  by  making  a framework  of  light  wood 
and  tacking  unbleached  cheesecloth  tightly  over  it.  Prints 
dried  in  this  manner  will  cur]  but  a trifle. 

164.  If  stretchers  are  not  to  be  had,  dry  the  prints,  face 
down,  on  clean,  uncolored  cloths  or  towels  which  are  free 
from  lint. 


46  MILITARY  PHOTOGRAPHY. 

165. - Never  dry  Velox  prints  between  blotters  or  on 
papers.  They  are  likely  to  stick  and  cause  much  annoy- 
ance. 

166.  For  mounting  with  paste  the  following  plan  is  best 
to  employ : 

After  prints  are  trimmed,  immerse  them  in  a tray  of 
clean  water,  allowing  them  to  soak  long  enough  to  become 
thoroughly  limp.  Remove  to  a good-sized  piece  of  clean 
glass,  placing  them  in  a pile,  face  down.  Cover  with  a 
piece  of  clean  blotting  paper,  and  with  a roller  squeegee 
press  all  the  superfluous  water  from  the  pile.  Then  with 
a good  bristle  paste  brush  apply  a thin,  even  coating  of 
starch  paste.  Raise  the  print  by  taking  hold  of  the  two 
opposite  corners  and  turning  it  over ; place  in  position  on 
the  mount.  Lay  a clean,  dry  blotter  over  the  print  and 
with  the  roller  press  into  contact.  Any  lint  or  fuzz  from 
the  blotter,  or  any  paste  on  the  surface  of  the  print,  should 
be  immediately  removed  with  a soft  sponge  or  dampened 
cloth.  When  dry,  shape  the  mounted  print  by  running  it 
through  a cold  burnisher.  Any  imperfections  in  the  fln- 
ished  print  may  be  corrected  by  spotting,  using  a flne  sable 
brush  and  spotting  color  of  india  ink. 

HOW  TO  MAKE  PRINTS  FROM  WET  NEGATIVES. 

167.  The  negative  must  be  thoroughly  washed  and  freed 
from  any  trace  of  Hypo.  Immerse  a piece  of  Velox  paper 
in  clean  water  for  a few  seconds,  then,  placing  it  on  the 
film  side  of  the  wet  negative,  squeegee  it  carefully  so  as  not 
to  break  the  film.  Expose  without  the  use  of  a printing 
frame.  After  exposure,  place  both  negative  and  paper  in 
water,  allowing  them  to  soak  for  a moment  before  trying 
to  separate  them.  Develop  and  fix  the  print  in  the  usual 
way. 

C.  P.  M.  C.  BROMIDE  PAPER. 

168.  Read  directions  carefully  before  using. 

The  exposure  of  P.  M.  C.  bromide  paper  varies  with  the 
density  of  the  negative  and  the  quality  and  intensity  of  the 
light  used. 


MliLITAEY  PHOTOGRAPHY. 


47 


Developer. 


Avoirdupois. 

Metric. 

Amidol 

60  grains 

Grams. 

4 

Sulphite  soda,  granular 

1 ounce  or  hydrometer  test,  14 . 
.S2  ounces 

30 

Water 

1,000 

169.  To  every  8 ounces  ready  developer  add  20  minims 
of  a 10  per  cent  solution  of  bromide  of  potassium.  It 
may  be  used  several  times  in  succession,  provided  it  re- 
mains clear.  For  very  strong  negatives  the  bromide  of 
potassium  should  be  omitted  and  the  developer  weakened 
by  increasing  the  amount  of  water.  For  soft,  weak  nega- 
tives the  quantity  of  bromide  of  potassium  may  be  doubled. 

170.  With  this  developer  no  clearing  solution  is  neces- 
sary ; as  soon  as  the  print  is  fully  developed  rinse  off  with 
two  or  three  changes  of  fresh  water  and  inmiediately  place 
in  the  following : 

FIXING  BATH. 

Water 64  ounces. 

Hypo  soda 8 ounces. 

171.  It  is  advisable  to  mix  this  up  several  hours  before 
using,  or,  better  still,  the  night  before.  The  use  of  a 
freshly  made  fixing  bath  is  frequently  the  cause  of  blister- 
ing. 

172.  An  acid  fixing  bath  will  yield  clearer  and  more 
brilliant  prints  than  a neutral  or  alkaline  bath ; to  accom- 
plish this  add  5 minims  of  acetic  acid  to  every  ounce  of 
hyposulphite  of  soda  used.  Alum  may  be  substituted  in 
place  of  the  acetic  acid,  as  it  also  serves  the  purpose  of 
toughening  the  film.  In  using  alum,  add  one-quarter 
ounce  to  every  2 ounces  of  hypo  soda. 

NOTES. 

173.  Weak,  light  prints  are  the  result  of  under  exposure, 
or  from  the  use  of  an  exhausted  developer. 

174.  Dark,  muddy,  or  mealy  prints  are  caused  by  over- 
exposure. 

175.  For  best  results  it  is  advisable  to  use  a fresh  fixing 
bath  every  day. 


48 


MILITARY  PHOTOGRAPHY. 


AZO  DEVELOPING  POWDEES. 

(For  bromide  papers.) 

176.  Ready  for  use. 

Twelve  powders,  sufficient  for  48  ounces  ready  devel- 
oper. 

Six  powders,  sufficient  for  24  ounces  ready  developer. 

Pull  directions  accompany  each  package. 

DIRECTIONS. 

177.  The  Eastman  Co.  recommends  amidol  or  metol 
hydro  developer  for  use  with  all  of  its  bromide  papers. 

AMIDOL  DEVELOPER. 

(Concentrated  solution.) 

178.  The  concentrated  stock  solution  is  prepared  by 
dissolving  in  succession  in : 


12  ounces Water. 

ounces Sulphite  soda,  des. 

^ ounce Amidol. 


179.  Enough  of  this  stock  solution  should  be  prepared 
at  one  time  for  only  one  day’s  use. 

TO  DEVELOP. 

180.  Take  in  a suitable  tray: 


Concentrated  stock  solution ounces. 

10  per  cent  solution  bromide  of  potassium 8 drops. 

Water 6 ounces. 


METOL  HYDRO  DEVELOPER. 

(Concentrated  solution.) 


48  ounces Water. 

^ dram Metol. 

10  drams Sulphite  soda,  des.' 

2 drams Hydroquinone. 

1 dram Bromide  of  potassium. 

20  drams Carbonate  soda,  des. 


181.  If  sulphite  and  carbonate  sodas  in  crystal  form 
are  substituted  for  desiccated,  double  the  quantities  men- 
tioned should  be  used. 


MILITARY  PHOTOGRAPHY. 


49 


TO  DEVELOP. 

182.  Take  in  a suitable  tray : 


Concentrated  solution 4 ounces. 

Water 4 ounces. 


183.  Use  developer  at  a temperature  of  about  70°  P. 
After  exposure,  soak  the  paper  in  water  until  limp  and 
brush  lightly  over  the  surface,  while  wet,  with  a tuft  of 
cotton  and  flow  developer  over  the  print. 

184.  The  image  should  appear  slowly  and  should  de- 
velop up  strong,  clear,  and  brilliant.  When  the  shadows 
are  sufficiently  black,  pour  off  the  developer  and  rinse  the 
print  thoroughly  with  pure  water.  Increasing  the 
amounts  of  bromide  potassium  given  in  the  formulae  is 
sometimes  necessary  to  prevent  grayish  high  lights. 

185.  Immerse  prints  for  10  minutes  in  the 

FIXING  BATH. 


Hyposulphite  soda 3 ounces. 

Water 16  ounces. 


186.  After  fixing,  wash  thoroughly  for  two  hours  and 
hang  up  to  dry. 

187.  A fresh  fixing  bath  should  fix  twenty-four  8 by  10 
prints  or  equivalent. 

IMPORTANT  DETAILS. 

188.  Clean  dishes  and  clean  hands. — The  faintest  trace 
of  hyposulphite  of  soda  or  of  pyrogallic  acid  is  fatal  to 
good  results  with  bromide  paper,  and  the  operator  can  not 
be  too  careful  to  avoid  any  contaminations. 

189.  Do  not  use  amidol  solution  that  is  more  than  24 
hours  old. 

190.  Fresh  hypo  solution  is  required  for  fixing  each 
batch  of  prints. 

191.  The  washing  must  be  thorough  after  fixing. 

192.  Blisters  sometimes  appear  in  bromide  paper,  and 
may  be  avoided  by  using  a little  common  salt  in  the  first 
washing  water  after  fixing. 

193.  Mealy  prints  are  caused  by  overexposure. 


50 


MILITARY  PHOTOGRAPHY. 


194.  Other  developers  (except  pyrogallic  acid)  may  be 
used  to  develop  Eastman’s  bromide  papers,  formulas  for 
the  use  of  which  accompany  the  chemicals. 

195.  Small  white  spots  and  streaks  are  caused  on  matte- 
enamel  and  platino  papers  by  developer  not  taking  evenly. 
To  overcome,  before  pouring  developer  on  print  take  a 
camel’s-hair  brush  or  piece  of  cotton  and  brush  over  the 
whole  print  while  it  is  immersed  in  water. 

CONTACT  PRINTING. 

196.  Gas,  lamp  or  candle  light  may  be  used.  Strong, 
intense  negatives  are  best  printed  by  strong  light. 

197.  The  exposure  varies  with  the  intensity  of  the  nega- 
tive and  the  quality  and  intensity  of  the  light,  but  may  be 
approximately  stated  to  be,  using  as  thin  a glass  negative 
or  film  as  will  make  a good  print,  1 second  by  diffused  day- 
light, or  10  seconds  at  a distance  of  1 foot  from  a No.  2 
kerosene  burner. 

XI.  MISCELLANEOUS. 

A.  FORMULA  FOR  SENSITIZING  BLUE-PRINT  PAPER. 

198.  Prepare  the  following  solutions  separately: 


1.  Water 8 ounces. 

Red  prussiate  of  potash ounces. 

2.  Water 8 ounces. 

Iron  and  ammonium  citrate 2 ounces. 


Mix  equal  parts  of  the  above  solutions  together. 

B.  FIXING  BOTH  FOR  MADURA  PAPER. 


Water 8 ounces. 

Hyposulphite  of  soda 1 ounce. 


C.  STARCH  PASTE. 

199.  Ordinary  gloss  starch  dissolved  in  just  enough  cold 
water  to  make  a thick  solution  is  prepared,  and  enough 
boiling  water  poured  into  it  so  that  it  thickens  in  a clear, 
translucent  jelly.  Set  aside  and  when*  cool  remove  the 
skin  which  forms  and  use  the  clear  paste. 


MILITAEY  PHOTOGRAPHY. 


51 


XII.  MILITARY  USES  OF  PHOTOGRAPHY.i 

200.  In  military  operations  photography  will  find  its 
principal  use  in  obtaining — 

(a)  Views  forming  a key  for  range  charts. 

(h)  Views  to  illustrate  reports  of  operations  and 
reconnaissance  parties. 

(c)  Views  to  illustrate  conditions  at  points  where 
special  engineer  operations  (bridge  or  rail- 
way construction,  etc.)  are  likely  to  be 
necessary. 

{d)  Accurate  perspective  representations  of  the 
prominent  features  of  the  landscape  to  be 
used  as  a basis  for  control  of  military  maps. 

{e)  Photographs  taken  from  aeroplanes,  for  the 
location  of  new  iDOsitions  of  enemy’s  bat- 
teries, intrenchments,  etc. 

201.  For  the  purposes  under  the  heads  (a)  and  (6), 
free-hand  outline  perspective  sketches  are  preferable  to 
photographs;  because  the  mass  of  detail  and  prominent 
unimportant  objects  in  the  foreground,  appearing  in  pho- 
tographs, obscure  the  details  of  the  background  which  are 
usually  of  greater  military  importance.  However,  the 
taking  of  a photograph  requires  a much  shorter  occupa- 
tion of  the  observing  point  and  an  expert  sketcher  is  not 
needed  for  the  purpose. 

202.  To  be  of  an}^  military  value,  views  coming  under 
the  headings  (a),  (&),  and  (c)  must  permit  of  accurate 
orientation  of  the  photograph  on  available  maps  and  in 
this  regard  they  should  comply  with  the  requirements  as 
to  the  direction  of  the  axis  and  leveling  of  the  camera 
prescribed  hereafter  for  photographic  surveying. 

203.  In  the  presence  of  the  enemy  a survey  or  recon- 
naissance party  will  reach  a point  beyond  which  the  country 
can  not  be  traversed.  The  locus  of  such  points  sets  a prac- 
tical limit  to  the  extension  of  mapping  operations  in  the 
original  manner;  but  if  accurate  perspective  representa- 

1 The  parts  of  this  chapter  on  photographic  surveying  are  based  on  Chapter  VI  of 
“ Higher  Surveying,”  by  Breed  and  Hosmer.  ^ _ 


52 


MILITARY  PHOTOGRAPHY. 


tions  of  the  ground  seen  from  a series  of  points  along  this 
limiting  line  he  procured,  a fairly  accurate  map  of  the 
inaccessible  terrain  may  be  plotted  by  resection  from  the 
perspective  pictures.  The  photographic  camera  offers  a 
way  of  obtaining  quickly  and  mechanically  such  a series 
of  perspective  pictures.  The  rapidity  and  accuracy  with 
which  this  map  can  be  plotted  will  depend  upon  the  care 
with  which  the  camera  positions  were  selected,  the  pre- 
cision of  the  adjustment  and  orientation  of  the  instrument 
for  each  view,  and  the  skill  and  facility  (gained  by  experi- 
ence) of  the  draftsman. 

204.  The  issue  cameras  can  be  used  for  such  photo- 
graphic surveys  as  may  be  required  during  military  opera- 
tions without  other  special  apparatus  than  an  improvised 
device  for  leveling  the  instrument.  A simple  manner  of 
providing  for  this  consists  in  mounting  the  camera  rigidly 
to  a board  provided  with  three  leveling  screws,  at  the 
vertices  of  an  equilateral  triangle,  and  two  spirit  levels, 
one  at  right  angles  to  the  plane  of  the  film  or  plate  and 
the  other  parallel  to  this  plane.  The  camera  so  mounted 
can  then  be  laid  on  the  Engineer  sketching  board,  which 
should  be  approximately  leveled  by  adjustment  of  the 
tripod. 

205.  Occasions  ma}^^  arise  when  a map  of  the  terrain  in 
rear  of  the  firing  line  is  required  and  the  nature  of  the 
country  is  such  as  to  make  ordinary  instrumental  survey 
methods  very  slow  or  very  expensive.  Under  these  cir- 
cumstances photographic  survey  methods  may  prove  a 
convenient  solution  of  the  problem. 

206.  Special  terms, — The  relationship  existing  between 
points  in  the  landscape,  the  film  or  plate  of  the  camera, 
and  the  photograph  is  diagrammatically  indicated  in 
figure  9. 

The  actual  points  on  the  ground  are  indicated  by  L 
and  L'. 

Their  position  on  the  film  or  plate  (negative)  is  indicated 
by  N and  N'. 

The  position  of  the  same  points  in  the  photographic 
print  is  indicated  by  P and  P'. 


MILITARY  PHOTOGRAPHY. 


53 


The  optical  center  of  the  lens  is  indicated  by  O. 

The  focal  distance  of  the  camera  is  the  normal  distance 
from  O to  the  plane  N N'. 

The  horizon  line  is  the  intersection  of  a level  plane 
through  the  point  0 and  the  plane  of  the  photograph 


(P  P'). 


The  principal  line  is  the  intersection  with  the  plane 
of  the  photograph  of  a vertical  plane  perpendicular  to 
the  plane  of  the  picture. 


Fig.  9. 


The  principal  point  is  the  intersection  on  the  photo- 
graph of  the  horizon  line  with  the  principal  line. 

207.  Camera  positions, — Camera  positions  must  be  so 
selected  that  prominent  points  appear  in  at  least  one  pic- 
ture from  each  of  two  camera  stations.  For  check  as  to 
accuracy  of  the  work,  all  camera  stations  should  appear 
in  photographs  taken  from  at  least  three  other  camera 
stations,  and  if  a few  other  prominent  points  can  also 
appear  in  three  views  the  accuracy  of  the  map  will  be 
enhanced.  The  best  location  for  a camera  station  is  the 
top  of  a hill,  moderately  high,  about  halfway  between  the 
lowest  ground  and  the  highest  part  of  the  sky  line.  Ex- 
tremely high  camera  positions  will  crowd  too  much  of 
the  terrain  into  the  lower  half  of  the  picture  and  too  low 


54 


MILITAEY  PHOTOGRAPHY. 


a position  will  restrict  the  view,  because  of  interference 
of  objects  in  the  foreground. 

208.  Constants  and  adjiistmeMts, — Having  provided  the 
camera  with  a means  of  leveling  it,  the  following  adjust- 
ments and  determinations  of  instrumental  constants  are 
necessary : 

209.  Adjustments  of  the  bubble  which  is  perpendicular 
to  the  plane  of  the  film. — The  bubble  which  is  perpendicular 
to  the  plane  of  the  film  or  plate  should  be  so  adjusted  that 
when  the  plate  is  vertical  the  bubble  is  central ; or  else  a 
reading  of  the  bubble  should  be  noted  which  corresponds  to 
the  vertical  position  of  the  plate,  and  this  position  of  the 
bubble  should  be  marked  in  some  way  on  the  glass  tube. 
To  determine  the  vertical  position  of  the  plane  of  the  film 
set  up  a leveling  instrument  in  front  of  and  at  the  same 
height  as  the  camera  and  find  some  distant  point  which 
is  on  the  horizontal  cross  hair.  Turn  the  level  around  on 
its  vertical  axis  until  it  points  toward  the  camera.  Level 
the  camera  and  place  a ground  glass  plate  or  a piece  of 
tracing  paper  accurately  in  the  position  ordinarily  occu- 
pied by  the  film  or  plate.  Turn  the  camera  so  that  the 
reflection  of  the  distant  object  from  the  back  surface  of 
the  plane  of  the  film  can  be  seen  through  the  telescope  of 
the  leveling  instrument.  If  the  plane  of  the  film  is  ver- 
tical the  image  of  this  object  will  appear  somewhere  on 
the  horizontal  cross  hair  of  the  leveling  instrument;  if 
it  is  not,  the  camera  must  be  tilted  until  this  condition  is 
fulfilled.  Then  the  level  tube  may  be  adjusted;  if  it  is 
not  adjustable,  the  scale  readings  of  the  ends  of  the  bubble 
must  be  noted  or,  preferably,  marked  in  some  way  on  the 
tube. 

210.  The  camera  may  then  be  placed  on  the  tripod  so 
that  the  long  dimension  of  the  plate  is  vertical,  and  a 
similar  adjustment  of  the  level  perpendicular  to  the  plate 
may  be  made  for  this  position  of  the  camera. 

211.  Determining  the  position  of  the  principal  point. — 
After  the  bubbles  are  adjusted  so  that  the  plate  can  be 
made  vertical,  a transit  or  a leveling  instrument  is  set  up 
and  leveled,  and  two  well-defined  points  on  the  horizon  are 


MILITARY  PHOTOGRAPHY. 


55 


found  which,  when  photographed  on  one  plate,  will  come 
near  its  opposite  edges.  The  camera  is  set  at  the  same 
height  as  the  leveling  instrument,  with  the  long  axis  of  the 
film  horizontal ; the  level  bubble  which  is  perpendicular  to 
the  plane  of  the  film  is  then  centered  and  a plate  or  film 
is  exposed.  A line  drawn  on  the  negative  through  the  pho- 
tographs of  these  points  determines  a horizontal  line.  The 
camera  is  now  placed  on  the  tripod  at  right  angles  to  its 
first  position  (with  long  axis  of  the  film  vertical)  and  the 
operation  repeated,  two  new  points  at  the  same  height  as 
the  camera  being  selected,  if  necessary,  to  bring  them  with- 
in the  limits  of  the  picture.  A line  through  the  points  on 
the  second  negative  is  a horizontal  line  for  this  second  po- 
sition. The  line  on  the  second  negative  may  now  be  trans- 
ferred to  the  first  one  by  means  of  measurements  made 
along  the  edges  of  the  exposed  portion  of  the  plate  or  film. 
The  intersection  of  these  two  lines,  both  of  which  are  now 
on  the  same  negative,  will  determine  the  position  of  the 
principal  point.  Since  the  bubbles  which  are  parallel  to 
the  plate  have  not  been  adjusted  these  two  lines  are  not 
necessarily  at  right  angles  to  each  other. 

212.  In  case  it  is  impossible  to  find  distinct  points  ex- 
actly on  the  true  horizon,  any  well-defined  points  (prefer- 
ably near  the  horizon)  may  be  chosen  and  vertical  angles 
may  be  measured  to  these  points.  The  vertical  distance  on 
the  print  from  these  points  to  the  horizon  line  may  be  com- 
puted by  use  of  the  azimuths,  vertical  angles,  and  the  focal 
distance.  If  these  vertical  distances  are  laid  off  on  the 
print  they  will  give  a series  of  points  which  will  be  on  the 
true  horizon. 

213.  Determining  the  positions  of  horizon  and  principal 
lines. — Now  that  the  principal  point  has  been  determined 
the  horizontal  and  principal  lines  may  be  laid  out  by 
means  of  measurements  along  the  edges  of  the  exposed 
part  of  the  plate  or  film.  If  the  arrangement  of  the 
camera  permits,  a black  paper  or  wooden  frame,  the  inside 
edges  of  which  will  limit  the  amount  of  plate  or  film 
exposed,  should  be  inserted  in  front  of  and  against  the 
plate  or  film.  Notches  in  the  inside  edges  of  this  frame. 


56 


MILITARY  PHOTOGRAPHY. 


which  will  appear  in  the  photograph,  should  now  be  cut 
to  indicate  the  extremities  of  the  two  lines  perpendicular 
to  one  another  which  intersect  at  the  principal  point.  The 
horizon  and  principal  lines  may  then  be  drawn  on  any 
print  by  simply  joining  by  straight  lines  on  the  print  the 
photograph  of  these  notches. 

214.  Adjustment  of  the  bubble  which  is  parallel  to  the 
plane  of  the  film. — The  level  which  is  parallel  to  the  plane 
of  the  film  should  be  so  adjusted  as  to  be  central  when 
the  horizon  line  is  truly  horizontal,  or  else  a reading  on 
the  level  bubble  should  be  found  which  corresponds  to  this 
horizontal  position. 

This  may  be  done  by  tipping  the  camera  until  the  bubble 
is  at  one  end  of  the  tube  and  then  taking  a photograph 
of  the  points  which  have  already  been  used  in  fixing  the 
horizon  line.  This  wull  show  the  horizon  line  inclined  to 
the  actual  horizon.  The  camera  is  then  inclined  until 
the  bubble  is  at  the  other  end  of  its  tube,  and  another  plate 
is  exposed.  This  second  plate  will  also  show  the  horizon 
line  inclined  to  the  true  horizon,  but  in  the  opposite  direc- 
tion. The  exact  position  of  the  level  bubble  should  be 
noted  in  each  case.  After  measuring  on  the  edges  of  the 
plate  the  distance  from  each  notch  to  the  horizon  as  de- 
termined by  the  photographed  points,  simple  interpola- 
tion between  the  bubble  readings  and  between  the  meas- 
ured distances  will  show  what  the  bubble  should  read 
when  the  horizon  line  defined  by  the  notches  is  level.  If 
the  level  is  adjustable  the  bubble  should  be  made  central 
while  the  camera  is  in  the  correct  position.  During  the 
above  adjustment  the  plate  should  be  kept  vertical  by 
means  of  the  bubble  which  is  perpendicular  to  the  plate. 

215.  Determining  the  focal  length  of  the  lens. — The 
focal  length  is  usually  given  by  the  instrument  maker, 
but  it  may  be  found  in  the  field  by  either  of  the  following 
methods. 

216.  First  method.^ — Set  a transit  over  the  camera  sta- 
tion and  measure  the  angle  AOB  between  two  distant 

1 This  is  the  method  given  hy  Capt.  E.  Deville,  surveyor  general  of  dominion  lands,  in 
“ rhotographic  Surveying,”  published  by  the  Government  I’rinting  Bureau  at  Ottawa. 


MILITARY  PHOTOGRAPHY. 


57 


points  A and  B.  In  figure  10  let  AOB=a+P=«.  Expose 
a plate  and  measure  on  tlie  negative  the  distance  x and  y 


from  the  points  a and  b to  the  principal  line  at  c.  Let 
f=Oc.  Then 


and 


hence 


tan  ct — £ 
tan  j 


xy 

tan  a tan  /5=^ 


tan  (a+j8)=tan  co: 


?+z 

f^f 

l-S 

£2 


. f_xy=o 

tan  CO 


Solving  this  equation  gives 

f=jLty_  + 

2 tan  CO 


V 


(x+y)^ 

4 tan^co 


■xy 


58 


MILITARY  PHOTOGRAPHY. 


217.  Second  method. — Set  np  the  camera  and  level  it; 
set  two  poles,  or  select  two  well-defined  points,  A and  B, 
figure  11,  on  the  same  level  as  the  camera,  the  two  being 
equally  distant  from  the  camera,  and  photograph  them. 
The  angle  AOB  should  not  he  very  acute  if  an  accurate 
determination  of  the  focal  length  is  desired.  Measure  the 


Fig.  11. 


distances  AB,  cC,  and  ah.  The  first  two  should  be 
measured  with  a tape  and  the  third  scaled  from  a negative. 
Then 

CO+cO=cC 

and 

CO:  AB==cO:  ab 

From  these  equations  is  found  the  value  of  cO,  or  f. 
The  poles  should  be  far  enough  away  for  the  focus  to  be 
practically  the  same  as  it  will  be  for  the  surveying  work. 

218.  In  order  to  detect  distortion  in  the  photographic 
prints,  distances  equal  to  J f and  ^ f respectively  are  laid 
off  on  the  long  and  short  sides  of  the  rectangular  opening 
at  the  back  of  the  camera  and  marked  by  notches  similar 
to  those  used  in  marking  the  horizon  and  principal  lines. 
In  this  way  distances  of  J f and  \ f are  shown  on  all 
prints  and  any  change  in  the  dimensions  of  the  print  may 
be  measured  and  allowed  for. 


MILITARY  PHOTOGRAPHY. 


59 


219.  Plotting, — The  first  step  to  be  taken  in  preparing 
the  map  is  to  plot  the  camera  stations.  Before  any  of  the 
•details  can  be  plotted  it  is  necessary  to  locate  on  the  map 
the  position  of  the  picture  trace,  or  ground  line,  for  each 
photograph  taken.  This  trace  is  the  intersection  of  the 
picture  plane  with  the  plane  of  the  map  when  the  print 
is  vertical  and  at  a distance  from  the  camera  station  equal 
to  the  focal  length  of  the  lens,  and  in  such  a position  that 
every  point  on  the  print  has  its  proper  azimuth  from  the 
camera  station.  It  is  evident  that  when  the  print  is  in 
this  position  the  principal  plane  is  perpendicular  to  the 


print  and  that  the  picture  trace  is  tangent  to  a circle  with 
radius  f drawn  about  the  camera  station  as  a center.  In 
figure  12,  A represents  the  plotted  position  of  the  camera 
station;  B B'  is  a photograph  (lying  on  the  map)  taken 
from  A,  and  P P'  is  the  picture  trace.  If  the  print  is 
held  in  a vertical  position  on  the  picture  trace,  the  azi- 
muth of  every  point  on  the  print  as  seen  from  the  plotted 
position  of  the  camera  station  will  be  the  same  as  it  is 
in  the  field.  The  process  of  locating  the  picture  trace  is 
called  orienting  the  picture,  and  it  should  be  done  accu- 
rately, because  all  subsequent  plotting  from  this  picture 
will  depend  upon  this  location  of  the  trace. 


60 


MILITARY  PHOTOGRAPHY. 


220.  Orienting  the  picture  trace. — In  order  that  the  pic- 
ture trace  may  be  oriented  it  is  necessary  to  know  the  posi- 
tion of  the  horizon  and  principal  lines  and  also  the  focal 
length  of  the  lens.  In  addition  to  this  the  position  of  the 
camera  station  on  the  map  must  be  known  (from  previous 
survey  or  from  photographs  taken  from  other  camera  sta- 
tions, see  par.  259),  and  the  print  must  contain  the  photo- 
graph of  at  least  one  point  whose  direction  from  the  camera 
station  has  been  determined. 

221.  In  figure  13  suppose  that  a base  line  AB  has  been 
plotted  in  the  position  ab.  Let  the  focal  length  f equal 


be,  sometimes  called  the  distance  line.  About  a and  b as 
centers  draw  circles  of  radius  f . If  different  cameras  have 
been  used  at  the  two  stations  the  circles  must  each  have  a 
radius  equal  to  the  value  of  f for  the  camera  used.  . The 
focal  length  laid  off  must  be  the  actual  length,  no  matter 
what  scale  is  chosen  for  the  map.  Let  us  suppose  that 
the  first  photograph  taken  from  station  B includes  the 
picture  A and  let  figure  14  be  the  print  so  taken.  Any 
point  on  the  picture  may  be  projected  down  on  to  the 
picture  trace  by  means  of  a vertical  line,  and  so  far  as 
the  horizontal  location  of  points  is  concerned  it  may  be 


MILITARY  PHOTOGRAPHY. 


61 


considered  that  they  lie  on  the  picture  trace.  When  the 
picture  is  placed  in  position  the  principal  point  c on  the 
trace  (fig.  13)  must  be  on  the  circumference  of  the  circle 
about  b,  and  the  photographed  position  of  A must  be 
somewhere  on  the  line  ba,  produced  if  necessary.  To  find 
the  position  of  the  picture  trace,  erect,  a'  c'  perpendicular 
to  ba',  scale  from  the  print  the  distance  cA'  (fig.  14),  and 
lay  it  off  on  this  perpendicular ; this  gives  point  c'.  Draw 
a line  from  c'  to  the  center  b.  Point  c,  where  the  line 
cuts  the  circle,  is  the  center  of  the  picture  trace.  Through 


A' 

c 

♦< 

• 

Fig.  14. 


c draw  a line  perpendicular  to  be ; this  is  the  picture  trace. 
Point  A"  is  the  position  on  the  picture  trace  PcP'  corre- 
sponding to  the  position  of  A on  the  ground.  PeP'  is  the 
jucture  trace  desired,  because  it  is  perpendicular  to  the 
principal  plane  be  at  point  c ; and  c is  the  principal  point 
because  cA"=c'  a'  (fig.  13)=cA'  as  scaled  from  the  print 
(fig.  14). 

222.  A second  picture  trace  may  be  located  from  this  one 
if  there  is  on  the  right  side  of  this  first  picture  some  point 
which  is  also  on  the  left  side  of  the  next  picture.  The  geo- 
metric construction  for  locating  the  second  photograph  is 


62 


MILITARY  PHOTOGRAPHY. 

similar  to  that  used  in  orienting  the  first.  In  figure  13,  T is 
a point  which  appears  on  two  adjacent  prints,  PP'  and 
QQ'.  The  trace  QQ'  is  determined  on  the  map  by  means 
of  point  t',  which  is  the  position  of  T on  the  trace  PP'. 
Where  the  line  tb  cuts  the  circle  at  k erect  a perpendicular 
kca',  the  distance  kc2'  being  obtained  from  the  second  pho- 
tograph just  as  a'  c'  was  obtained  from  the  print  shown  in 
figure  14.  The  line  C2'b  cuts  the  circle  at  C2,  which  is  the 
principal  point  of  the  second  picture  trace.  The  line  bt 
cuts  QQ'  at  t,  which  is  the  position  of  T on  the  second 
trace. 

223.  In  case  the  focal  length  of  the  lens  is  not  known, 
or  if  it  is  desired  to  verify  its  length,  the  picture  trace 
may  be  located  by  the  following  method,  provided  that 
there  are  several  points  shown  in  the  print  wdiich  have 
been  connected  with  triangulation  points  by  measured 
horizontal  angles.  On  the  straight  edge  of  a strip  of  paper 
mark  a point  representing  the  trace  of  the  principal  line 
and  from  this  point  lay  off  the  distance  from  the  princi- 
pal line  to  each  of  the  points  to  which  angles  have  been 
measured.  Draw  radial  lines  on  the  plan  from  the  camera 
station  toward  the  points  sighted  with  the  transmit,  using 
the  measured  angles  to  obtain  the  direction  of  the  points. 
The  strip  of  paper  may  now  be  laid  on  the  plan  and  moved 
about  until  each  point  on  the  paper  lies  on  the  correspond- 
ing radial  line  on  the  plan.  This  position  of  the  edge  of 
the  paper  is  the  true  position  of  the  trace,  and  the  distance 
from  the  plotted  camera  station  to  the  principal  point  on 
the  strip  is  the  focal  length,  or  distance  line.  The  dis- 
tance line  should,  of  course,  be  perpendicular  to  the  trace. 
In  order  that  the  focal  length  may  be  determined  accu- 
rately by  this  method,  two  of  the  points  sighted  should  lie 
near  opposite  edges  of  the  print. 

224.  Since  the  prints  are  liable  to  become  distorted, 
measurements  which  must  be  obtained  with  great  accu- 
racy, such  as  those  for  obtaining  the  focal  length,  should  be 
scaled  directly  from  the  negative.  For  locating  details  it 
will  be  sufficientl.y  accurate  to  scale  f]*om  the  print  and  to 


MILITARY  PHOTOGRAPHY. 


63 


make  allowance  for  the  distortion  as  shown  by  the  notches 
on  the  edge  of  the  print. 

225.  In  the  field  the  labor  of  locating  the  trace  of  each 
picture  may  be  eliminated  by  construction  on  tracing 
paper  a camera  protractor  as  shown  in  figure  15,  drawn 
on  a piece  of  tracing  paper.  The  radius  of  the  circle=f. 
The  circumscribed  regular  polygon  is  selected  so  that  the 
length  of  each  side  is  a convenient  amount  less  than  the 
length  of  the  exposed  part  of  the  film  or  plate ; this  will 


insure  each  photograph’s  overlapping  adjacent  ones.  The 
line  NS  represents  a north  and  south  line.  On  occupying 
a camera  station  the  plane  table  sketching  board  is  set 
up  and  oriented  by  back  sights  to  known  objects.  The 
camera  protractor  is  then  laid  on  top  of  the  sketching 
board  and  oriented  on  the  map  with  the  help  of  the  NS 
line.  Photographs  are  then  taken,  placing  the  camera  so 
that  the  film  or  plate  will  be  successively  parallel  to  the 
sides  1,  2,  3,  4,  etc.  This  is  most  easily  done,  if  the  board 
(on  which  the  camera  is  mounted  for  leveling)  be  finished 


64 


MILITARY  PHOTOGRAPHY. 


with  one  beveled  edge  parallel  to  the  plane  of  the  film. 
This  straight  edge  can  then  be  placed  for  each  photograph 
so  as  to  coincide  with  one  side  of  the  polygon  on  the  camera 
protractor.  To  plot  the  photographs  it  is  only  necessary 
to  orient  the  camera  protractor  over  the  plotted  position 
of  the  camera  station  and  to  prick  through  the  vertices  of 
the  polygon,  the  sides  of  which  are  the  traces  of  the  photo- 
graphs. 

226.  Locating  points  on  the  map. — Any  point  of  the  first 
picture  may  be  plotted  on  the  line  PcP'  (fig.  13)  by  scal- 
ing on  the  print  the  horizontal  distance  from  the  principal 
line  and  by  laying  off  this  distance  from  c on  the  trace 


PcP'.  By  drawing  lines  from  b to  the  points  thus  plotted 
on  the  picture  trace  a set  of  radiating  lines  is  obtained, 
showing  the  directions  of  these  points  as  seen  from  B,  and 
the  location  of  these  points  on  the  map  will  be  somewhere 
on  the  corresponding  radial  lines. 

227.  By  means  of  a photograph  from  A containing  these 
same  points  the  trace  of  this  photograph  may  be  oriented 
on  the  circle  about  a in  the  same  manner  as  that  described 
for  the  point  b.  (See  fig.  16.)  This  locates  these  same 
points  on  another  set  of  radiating  lines  drawn  from  a,  and 
the  intersection  of  corresponding  lines  from  a and  b,  such 
as  am  and  bm',  locates  the  point,  M,  on  the  map. 


MILITARY  PHOTOGRAPHY. 


65 


228.  Where  there  are  many  points  to  be  plotted  from 
one  base  line  a convenient  method  is  to  first  transfer  to 
the  straight  edge  of  a strip  of  paper  the  principal  point 
of  one  of  the  prints  and  to  lay  off  from  this  point  the 
distances  to  all  the  other  points  to  be  plotted.  This  paper 
can  be  fastened  in  the  proper  position  on  the  plan  to  serve 
as  the  picture  trace.  A similar  strip  is  constructed  for 
each  photograph  taken,  and  fastened  in  its  proper  place 
on  the  map.  Points  may  then  be  located  on  the  plan  by 
fastening  two  fine  threads  to  needles  stuck  in  the  end 
points  of  the  base  line,  passing  these  threads  through  cor- 
responding points  on  the  traces,  and  marking  the  inter- 
section on  the  plan. 

229.  Prom  the  points  so  located  the  details  may  be 
sketched,  the  topography  being  judged  from  the  appear- 
ance of  the  prints.  There  is  no  limit  to  the  number  of 
points  that  may  be  located,  provided  these  points  can  be 
positively  identified  on  the  prints.  Points  which  can  be 
identified  should  be  marked  with  the  same  numbers  on 
the  different  prints  for  convenience  in  plotting. 

230.  Determination  of  elevations  from  the  photo- 
graphs.— Differences  in  elevation  may  be-  found  graphi- 
cally or  by  computation,  the  former  being  the  more  com- 
mon method.  The  distance  of  a point  above  or  below  the 
horizon  line  may  be  scaled  from  the  print;  this  vertical 
distance  divided  by  the  horizontal  distance  from  the  plot- 
ted camera  station  to  the  point  on  the  trace  is  the  natural 
tangent  of  the  angle  of  elevation  or  depression.  It  is 
necessary  that  the  actual  horizontal  distance  from  the 
camera  to  the  point  should  be  known  before  the  elevation 
of  the  point  can  be  determined.  This  horizontal  distance 
may  be  scaled  from  the  map  after  the  point  has  been 
located  by  the  method  already  described.  The  difference 
in  elevation  between  the  camera  and  the  point  may  be 
found  by  simple  proportion  as  follows : 

231.  Figure  17  shows  the  plate  with  the  horizon  and 
principal  lines  drawn  upon  it.  A is  the  point  whose  eleva- 
tion above  the  camera  station  O is  desired.  Figure  18  is 


66 


MILITAKY  PHOTOGRAPHY. 


a portion  of  the  map,  O is  the  lens,  and  PP'  is  the  trace 
of  this  picture  on  the  map.  In  both  figures  17  and  18,  c is 
the  center  of  the  print,  B is  the  point  vertically  under  A, 
and  OB  is  the  horizontal  distance  from  O to  A.  If  in 
figure  18  a perpendicular  BA'  is  laid  off  at  B,  this  perpen- 
dicular being  equal  to  the  distance  AB  scaled  from  the' 
print,  then  the  angle  A'  OB  is  the  true  angle  of  elevation 
of  A above  a horizontal  plane  through  O.  The  plotted  po- 
sition of  A will  lie  on  the  line  OB  on  the  plan.  If  a is 
assumed  to  be  the  plotted  position  of  A,  and  aa'  is  drawn 


perpendicular  to  OB,  and  if  aa'  is  measured  with  the  same 
scale  as  that  used  in  laying  out  the  base  line,  the  result  will 
be  the  actual  difference  in  elevation  between  O and  A.  The 
distance  aa'  could  of  course  be  computed  by  proportion  if 
desired,  the  data  being  the  actual  distances  OB  and  BA 
in  inches  (OB  being  scaled  from  the  map  and  BA  from  the 
print)  and  the  distance  Oa  in  feet  as  scaled  froin  the  map. 

232.  Contours. — Contours  may  be  sketched  by  obtaining 
the  elevations  of  controlling  points  and  then  judging  the 
variations  in  slope  between  the  points  by  the  appearance 
of  the  photographs.  Sometimes  the  contours  are  first 


MILITARY  PHOTOGRAPHY. 


67 


sketcKed  on  the  photographs  by  making  use  of  the  eleva- 
tions already  determined,  and  then  these  contours  are 
drawn  on  the  map.  Since  there  is  a large  amount  of 


sketching  involved,  and  since  such  a map  must  be  gen- 
eralized to  a great  extent,  a knowledge  of  the  geological 
formation  of  the  country  will  be  of  great  assistance  in  de- 
termining the  characteristics  of  the  contours. 


O 


